[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 69.96%. Comparing base (8e645d2) to head (1e7c20e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9238      +/-   ##
==========================================
- Coverage   69.96%   69.96%   -0.01%     
==========================================
  Files         258      258              
  Lines       77927    77927              
  Branches    18974    18974              
==========================================
- Hits        54524    54521       -3     
+ Misses      17771    17759      -12     
- Partials     5632     5647      +15     

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