Remove cache alternate vector detach

[bneradt]

Cache alternate detach is a private helper with no current callers, and
its compaction loop contains a latent out-of-bounds read if the helper is
ever used. Keeping the dead path around preserves a future cache metadata
hazard without providing any current behavior.

This removes the unused helper and its declaration instead of repairing
the unreachable implementation. Existing alternate removal continues to
use the live remove path.

[Copilot]

Pull request overview

This PR removes the unused CacheHTTPInfoVector::detach() helper from the cache HTTP alternate vector implementation. The removed code path was dead (no callers) and contained a latent out-of-bounds read risk due to incorrect compaction logic, so deleting it reduces future maintenance and safety hazards without changing current behavior.

Changes:

• Removed the CacheHTTPInfoVector::detach(int idx, CacheHTTPInfo *r) declaration from P_CacheHttp.h.
• Removed the unused CacheHTTPInfoVector::detach() implementation from CacheHttp.cc.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/iocore/cache/P_CacheHttp.h	Drops the unused detach() method declaration from the internal cache alternate vector API.
src/iocore/cache/CacheHttp.cc	Deletes the dead detach() implementation (including the buggy compaction loop), leaving the existing remove() path as the sole alternate-removal mechanism.