[promptflow][internal] Remove TODO for SQLAlchemy silent warning (#1853)

# Description

Remove SQLAlchemy silent warning for 2.x as we already remove the upper
limit.

# All Promptflow Contribution checklist:
- [x] **The pull request does not introduce [breaking changes].**
- [ ] **CHANGELOG is updated for new features, bug fixes or other
significant changes.**
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- [ ] **Create an issue and link to the pull request to get dedicated
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workflow](../CONTRIBUTING.md#suggested-workflow).**

## General Guidelines and Best Practices
- [x] Title of the pull request is clear and informative.
- [x] There are a small number of commits, each of which have an
informative message. This means that previously merged commits do not
appear in the history of the PR. For more information on cleaning up the
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### Testing Guidelines
- [ ] Pull request includes test coverage for the included changes.

src/promptflow/promptflow/_sdk/_orm/session.py

@@ -32,10 +32,6 @@
     use_customized_encryption_key,
 )
 
-# silence RemovedIn20Warning to avoid unexpected warning message printed to users
-# TODO(2587221: migrate to SQLAlchemy 2.0)
-os.environ["SQLALCHEMY_SILENCE_UBER_WARNING"] = "1"
-
 session_maker = None
 lock = FileLock(LOCAL_MGMT_DB_SESSION_ACQUIRE_LOCK_PATH)