glapi: gl_table.py: remove unused variable 'es'
glapi: gl_table.py: remove unused variable 'es'

None of the three build systems ever set it, as such we can clear things
up a bit.

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>
Reviewed-by: Dylan Baker <91de990240e6abc00928035c476e6ad54ab72b92@gmail.com>
Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler