dispatch: stop generating separate GLES1 API code.

dispatch: stop generating separate GLES1 API code.

This patch removes the generated files api_exec_es1.c,
api_exec_es1_dispatch.h, and api_exec_es1_remap_helper.h (and the
source files and build rules used to generate them), since they are no
longer used.  GLES1 now uses the same dispatch table layout as all the
other APIs.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>