[vulkan] remove unused allocator release overload

[johningve]

The Vulkan allocator as well as the region and block allocators all had a int release(void *user_context) overload in addition to the regular int release(void *user_context, MemoryRegion *region). The single-argument overload is unused, and it is bug prone. It is easy to call the single-argument overload instead of the correct two-argument overload by forgetting to fill the user_context argument. This may not produce any compiler error because a pointer to a MemoryRegion converts implicitly to a void *.

Since the overload is unused, this commit removes it from the three allocator classes. Also in the block allocator, a private helper release_block_entry is also removed. Its only reference was the single-argument release.

Checklist

• Tests added or updated (not required for docs, CI config, or typo fixes)
• Documentation updated (if public API changed)
• Python bindings updated (if public API changed)
• Benchmarks are included here if the change is intended to affect performance.
• Commits include AI attribution where applicable (see Code of Conduct)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.33%. Comparing base (055bc89) to head (7273c2b).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9238      +/-   ##
==========================================
+ Coverage   70.24%   70.33%   +0.09%     
==========================================
  Files         255      255              
  Lines       78929    78904      -25     
  Branches    18879    18866      -13     
==========================================
+ Hits        55444    55498      +54     
+ Misses      17872    17857      -15     
+ Partials     5613     5549      -64     

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