Remove ImageCompressionAlgorithm::DisabledNoDecompress

[arpad-m]

Removes the ImageCompressionAlgorithm::DisabledNoDecompress variant. We now assume any blob with the specific bits set is actually a compressed blob.

The ImageCompressionAlgorithm::Disabled variant still remains and is the new default.

Reverts large parts of #8238 , as originally intended in that PR.

Part of #5431

[github-actions]

3042 tests run: 2927 passed, 0 failed, 115 skipped (full report)

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Flaky tests (2)

Postgres 15

• test_isolation[None]: debug
• test_pageserver_lsn_wait_error_safekeeper_stop: debug

Code coverage* (full report)

• functions: 32.6% (6938 of 21278 functions)
• lines: 50.0% (54528 of 109039 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
41e7909 at 2024-07-09T15:49:07.410Z :recycle:}