[eng] deprecate "multiapi" - Remove multiapi functionality from eng folder

[Copilot]

This PR deprecates and removes all "multiapi" related code, tools, and documentation from the eng folder as requested in the issue.

Changes Made

Deleted Files (958 lines removed)

• eng/tools/azure-sdk-tools/packaging_tools/multiapi_combiner.py - The main multiapi combiner tool (691 lines)
• eng/tools/azure-sdk-tools/packaging_tools/templates/multiapi_combiner/ - Complete template directory with 9 Jinja2 template files for multiapi code generation

Modified Files

• pyproject.toml - Removed multiapi_combiner script entry point
• sdk_generator.py - Removed multiapi-specific functions:
  • is_multiapi_package() - Function to detect multiapi packages
  • need_regen_for_multiapi_package() - Function to handle multiapi regeneration logic
  • Simplified package processing to treat all packages as single-api (isMultiapi=False)
  • Removed multiapi-specific conditional logic in sample cleanup
• package_utils.py - Removed is_multiapi parameter from change_log_generate() function and simplified logic
• test_servicemetadata.py - Removed multiapi test reference
• changelog_generics.md - Updated documentation to remove multiapi-specific section
• swagger_to_sdk_config_v4.json - Removed multiapi autorest configuration option

Impact

This change simplifies the SDK generation pipeline by:

• Removing 958 lines of multiapi-specific code
• Treating all packages consistently as single-API packages
• Eliminating the complexity of multiapi template generation
• Removing deprecated tooling while preserving all existing functionality for standard packages

The removal is backward-compatible as all packages will now be processed using the standard single-API generation path, which was already the recommended approach.

Fixes #42865.

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[Copilot]

Pull Request Overview

This PR removes the deprecated "multiapi" functionality from the Azure SDK for Python engineering tools and infrastructure. This includes deleting the multiapi combiner tool, templates, and all supporting code while simplifying the SDK generation pipeline to treat all packages consistently as single-API packages.

Key Changes

• Removes 958 lines of multiapi-specific code and templates
• Simplifies package generation logic to eliminate multiapi complexity
• Updates configuration files to remove multiapi options

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
multiapi_combiner.py	Deleted entire 691-line multiapi code generation tool
Template files	Removed 9 Jinja2 template files for multiapi generation
pyproject.toml	Removed multiapi_combiner script entry point
sdk_generator.py	Removed multiapi detection and processing functions
package_utils.py	Simplified changelog generation by removing multiapi parameter
Configuration files	Removed multiapi options from test and config files
changelog_generics.md	Updated documentation to remove multiapi section

[msyyc]

@scbedd Need one approval from code owner to merge. Please help review this PR, thanks!

[scbedd]

I ❤️ code simplification. Love the cleanup efforts @msyyc !

[msyyc]

/check-enforcer override