[codemod] Remove unused variables in caffe2/caffe2/video/video_decoder.cc (#122151)
Summary:
LLVM-15 has a warning `-Wunused-but-set-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused variables can compromise readability or, worse, performance.
This diff either (a) removes an unused variable and, possibly, it's associated code, or (b) qualifies the variable with `[[maybe_unused]]`, mostly in cases where the variable _is_ used, but, eg, in an `assert` statement that isn't present in production code.
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Test Plan: Sandcastle
Differential Revision: D54378401
Pull Request resolved: https://github.com/pytorch/pytorch/pull/122151
Approved by: https://github.com/Skylion007
