Cleanup README-related files in azure-rest-api-specs as part of AutoRest deprecation

## Problem

The current usage of readme.md in the azure-rest-api-specs repository has become outdated and unnecessarily complex. The readme.md files contain a mix of:

- SDK generation configuration
- Suppressions and validation-related settings
- Language-specific configuration (readme..md)
- Misc legacy or unused content

As we no longer generate SDK from readme or readme.language.md, this creates confusion for service teams and increases maintenance overhead.

## Proposal

Simplify and clean up README-related files across the repo with the following changes:

Keep only:

- tag definitions
- The files associated with each tag (input Swagger files, api-version grouping, etc.)
- Remove all unnecessary or legacy configurations and delete language-specific README files

Moving forward, this file could be the output of typespec autorest emitter so there is no need to spend human effort to maintain this file.

Review the readme.md and readme..md files across azure-rest-api-specs, focusing on the tag definitions, input Swagger files, and API-version grouping described in the proposal. Done means retaining tag-related content while removing SDK-generation, suppression, validation, language-specific, and other legacy configuration content.

Written by the indexing model from the issue text.