Remove some unused-but-set variables

Remove some unused-but-set variables

Detected by the -Wunused-but-set-variable option in the
open-source IntelLLVM (and, in theory, upstream Clang trunk).

There are also false-positive warnings there, so the
compilation log is noisy.
I'm not doing any silencing here, since it will, hopefully, change by
the time of Clang 13 release.
But the variables removed here appear to be genuinely unused.