tnl: Silence unused parameter warnings in _tnl_split_inplace

tnl: Silence unused parameter warnings in _tnl_split_inplace

Unused since db0eb3a437f ("vbo: Fix up in-place splitting for non-contiguous/indexed primitives.") which landed in 2010.

src/mesa/tnl/t_split_inplace.c: In function ‘_tnl_split_inplace’:
src/mesa/tnl/t_split_inplace.c:270:27: warning: unused parameter ‘min_index’ [-Wunused-parameter]
  270 |                    GLuint min_index,
      |                    ~~~~~~~^~~~~~~~~
src/mesa/tnl/t_split_inplace.c:271:27: warning: unused parameter ‘max_index’ [-Wunused-parameter]
  271 |                    GLuint max_index,
      |                    ~~~~~~~^~~~~~~~~

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4512>