Omit 2 ‘volatile’s in internal_lisp_condition_case

Omit 2 ‘volatile’s in internal_lisp_condition_case

* src/eval.c (internal_lisp_condition_case): Omit an unnecessary
‘volatile’ and an unnecessary pointer-to-volatile local var.
Perhaps these were needed in previous versions of Emacs, or to
pacify older versions of GCC when using --enable-gcc-warnings,
but they are not needed to pacify current GCC.

(cherry picked from commit c91c591f0f0cc774647c32bdcf05bb3a9551e340)