Python: Remove OpenAI plugin. Update OpenAPI exec params to use direct predicate reference

[moonbox3]

Motivation and Context

Dotnet had long removed the OpenAI plugin from its code base, and Python did not follow at the time. We had previously provided deprecation messages around using the OpenAI plugin and to switch to the OpenAPI plugin. We are now removing the OpenAI plugin from the SK Python SDK.

Additionally, there was a forward reference created without specifying the direct predicate context reference in the OpenAPIFunctionExecutionParameters. This put the burden on the dev to have to perform a model rebuild once the import was added. This PR cleans up the OperationSelectionPredicateContext import, which is now direct and via the sub-module and not via the parent module, which causes the init.py to load all dependencies (which is unnecessary).

Description

This PR:

• removes the unsupported OpenAI plugin (previously marked as deprecated)
• fixes the OperationSelectionPredicateContext import to allow a user to create the func exec params without receiving a pydantic error.
• updates unit tests to remove references to OpenAI plugin.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel/connectors/openapi_plugin
openapi_manager.py	80	8	90%	54, 71, 93–96, 141–142
openapi_parser.py	121	7	94%	67, 124, 188, 250–251, 254–255
semantic_kernel/functions
kernel_plugin.py	172	5	97%	392, 395, 424, 445, 470
TOTAL	16645	1769	89%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2991	4 💤	0 ❌	0 🔥	1m 27s ⏱️

[TaoChenOSU]

Question: This is a breaking change since we are removing features. Are we ok with breaking changes now?

[moonbox3]

Question: This is a breaking change since we are removing features. Are we ok with breaking changes now?

Valid question, but I would say yes because of two reasons:

1. OpenAI deprecated the OpenAI plugin, so there is no need for us to support it.
2. SK C# deprecated/removed this OpenAI plugin last March/April (of 2024), and we should have done it at the same time, but didn't.