[BUILD] Fix multiple assignment operators for SpinLockMutex

[SaiHarshaK]

Fixes #2500

Changes

Please provide a brief description of the changes here.
The multiple assignment operators for SpinLockMutex throws warnings in consumer build for these headers. This would require them to explicitly add #Pragma to ignore C4522.

This PR removes the redundant assignment to let the build pass without these warnings. Tested locally as I was able to repro this issue before this change.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: SaiHarshaK / name: Sai Harsha Kottapalli (a5108e2, 217a945, 2bbf0c0)
• ✅ login: ThomsonTan / name: Tom Tan (f677f68)

[ThomsonTan]

@SaiHarshaK thanks for the contribution. Please take a look and sign the EasyCLA.

[marcalff]

Thanks for the quick PR.

I would rather remove the volatile declaration instead,
and keep the regular one.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8f88553) 87.09% compared to head (2bbf0c0) 87.09%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2501   +/-   ##
=======================================
  Coverage   87.09%   87.09%           
=======================================
  Files         200      200           
  Lines        6103     6103           
=======================================
  Hits         5315     5315           
  Misses        788      788           

Files	Coverage Δ
api/include/opentelemetry/common/spin_lock_mutex.h	25.00% <ø> (ø)

[SaiHarshaK]

@marcalff I wasn't sure if there was any specific use case around why volatile was added in the first place, so assumed that might be the safer one to add.
I can certainly update this PR to use the other one.

[ThomsonTan]

Both declarations are marking the assignment operator as deleted instead of defining it. I am still not quite sure the reason of the triggered warning.

[SaiHarshaK]

Had to repush for clearing EasyCLA

[marcalff]

LGTM, thanks for the fix.

[ThomsonTan]

I didn't repro the warning with MSVC 19.38.33134, and also both overloads look correct to me, so could it be an issue for the specific MSVC @SaiHarshaK is using?

[SaiHarshaK]

Perhaps so, I don't have a way to currently update and check the same, since the infra on which build runs is out of my control.