Remove manual API tests superseded by GeneratedExamplesTest (#3402)

* Remove manual API tests superseded by GeneratedExamplesTest

These 62 manually maintained *ServiceTest.cs files tested CRUDL operations
that are now fully covered by GeneratedExamplesTest.cs, which was recently
updated to also generate async and autopaging test variants (sdk-codegen#3708).

Files testing SDK-specific behavior (file uploads, OAuth, webhook
verification, options serialization, sources, ephemeral keys, autopaging
infrastructure, etc.) are preserved.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Committed-By-Agent: claude

* Remove redundant options serialization tests

ContentEncoderTest.cs already covers all serialization mechanisms
generically (AnyOf, lists, nested objects, DateTime, StringEnum, etc.)
using synthetic TestOptions. These resource-specific tests add no
additional coverage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Committed-By-Agent: claude

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jar-stripe