[codemod] Remove unused-variable in /fbcode/pytorch/torchcodec/src/torchcodec/decoders/_core/VideoDecoder.cpp

[r-barnes]

Summary: [codemod] Remove unused-variable in {filename}

LLVM-15 has a warning -Wunused-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]].

buildsonlynotests - Builds are sufficient to verify

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Reviewed By: scotts

Differential Revision: D65445691

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D65445691