.Net Agents - Remove (Legacy) Experimental Agents Project and Samples (…

…#7979)

### Motivation and Context
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  1. Why is this change required?
  2. What problem does it solve?
  3. What scenario does it contribute to?
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New _Agent Framework_ is here:

[./dotnet/src/Agents](https://github.com/microsoft/semantic-kernel/tree/main/dotnet/src/Agents)

### Description
<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

Removing all legacy agent code and samples. This effort has been
superceded by the current _SK Agent Framework_.

Included "README" in place of the old project that points to the new
framework.

### Contribution Checklist
<!-- Before submitting this PR, please make sure: -->

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄

dotnet/SK-dotnet.sln

@@ -199,10 +199,6 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "AI", "AI", "{1B4CBDE0-10C2-
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Memory", "Memory", "{24503383-A8C4-4255-9998-28D70FE8E99A}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Experimental.Agents", "src\Experimental\Agents\Experimental.Agents.csproj", "{5438D1E3-E03D-444B-BBBA-478F93161AA8}"
-EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Experimental.Agents.UnitTests", "src\Experimental\Agents.UnitTests\Experimental.Agents.UnitTests.csproj", "{4AD80279-9AC1-476F-8103-E6CD5E4FD525}"
-EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Experimental.Orchestration.Flow", "src\Experimental\Orchestration.Flow\Experimental.Orchestration.Flow.csproj", "{B0CE8C69-EC56-4825-94AB-01CA7E8BA55B}"
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Experimental.Orchestration.Flow.IntegrationTests", "src\Experimental\Orchestration.Flow.IntegrationTests\Experimental.Orchestration.Flow.IntegrationTests.csproj", "{3A4B8F90-3E74-43E0-800C-84F8AA9B5BF3}"
@@ -567,18 +563,6 @@ Global
 		{3FC4A81B-8ABE-473F-BC7C-6F4885775534}.Publish|Any CPU.Build.0 = Debug|Any CPU
 		{3FC4A81B-8ABE-473F-BC7C-6F4885775534}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{3FC4A81B-8ABE-473F-BC7C-6F4885775534}.Release|Any CPU.Build.0 = Release|Any CPU
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8}.Publish|Any CPU.ActiveCfg = Publish|Any CPU
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8}.Publish|Any CPU.Build.0 = Publish|Any CPU
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8}.Release|Any CPU.Build.0 = Release|Any CPU
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525}.Publish|Any CPU.ActiveCfg = Debug|Any CPU
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525}.Publish|Any CPU.Build.0 = Debug|Any CPU
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525}.Release|Any CPU.Build.0 = Release|Any CPU
 		{B0CE8C69-EC56-4825-94AB-01CA7E8BA55B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{B0CE8C69-EC56-4825-94AB-01CA7E8BA55B}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{B0CE8C69-EC56-4825-94AB-01CA7E8BA55B}.Publish|Any CPU.ActiveCfg = Publish|Any CPU
@@ -906,8 +890,6 @@ Global
 		{3FC4A81B-8ABE-473F-BC7C-6F4885775534} = {A21FAC7C-0C09-4EAD-843B-926ACEF73C80}
 		{1B4CBDE0-10C2-4E7D-9CD0-FE7586C96ED1} = {0247C2C9-86C3-45BA-8873-28B0948EDC0C}
 		{24503383-A8C4-4255-9998-28D70FE8E99A} = {0247C2C9-86C3-45BA-8873-28B0948EDC0C}
-		{5438D1E3-E03D-444B-BBBA-478F93161AA8} = {A2357CF8-3BB9-45A1-93F1-B366C9B63658}
-		{4AD80279-9AC1-476F-8103-E6CD5E4FD525} = {A2357CF8-3BB9-45A1-93F1-B366C9B63658}
 		{B0CE8C69-EC56-4825-94AB-01CA7E8BA55B} = {A2357CF8-3BB9-45A1-93F1-B366C9B63658}
 		{3A4B8F90-3E74-43E0-800C-84F8AA9B5BF3} = {A2357CF8-3BB9-45A1-93F1-B366C9B63658}
 		{731CC542-8BE9-42D4-967D-99206EC2B310} = {A2357CF8-3BB9-45A1-93F1-B366C9B63658}