Remove the "Requirement" field from the Text Generator node

[shige]

Task description

Remove the "Requirement" field from the Text Generator node.

Background

Currently, the "Requirement" field in the Text Generator node is often ineffective at influencing the generated text. Users find that instructions provided in the "Instruction" or "Source" fields are more reliably followed. This forces users to either disregard the "Requirement" field or use a workaround of excluding it via a system prompt every time they use the node.

TODO (Optional)

• Remove the "Requirement" field from the Text Generator Node.
• Ensure that existing workflows that may have used the "Requirement" field are not broken or produce errors.
• Update the documentation to reflect the change.

Additional notes (Optional)

This change aims to streamline the user experience with the Text Generator node by removing a field that is consistently proving to be less effective and adding an unnessecary layer to configure.

[kentaro-m]

I'll do it.