Remove many test cases that never run because maxColorAttachments=8

[kainino0x]

Our team noticed these because they were spamming a ton of output to the test logs.

These cases were trying to test more than 8 color attachments, but all of these tests run against the default adapter so maxColorAttachments is always 8.

Unfortunately it's hard to exactly test this because Dawn never exposes more than 8 color attachments. (But it does expose 4 in compat, and those still work.) Anyway I'm pretty certain by inspection that none of these tests ever request higher limits.

As an aside, reduces the verbosity of the subcase names in attachment_compatibility.spec.ts.

Issue: None, but introduces some TODOs for #3363

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

When landing this PR, be sure to make any necessary issue status updates.

[greggman]

Should this rather change to use MaxLimitsTestMixin?

[greggman]

Sorry, Didn't bother to look in detail. I see this is a temp fix and is listed as a TODO to make it the correct fix. I'll review as is.

[greggman]

lgtm