configure.ac: remove src/gallium/winsys/intel/drm/Makefile reference
configure.ac: remove src/gallium/winsys/intel/drm/Makefile reference

Not wired up (not referenced in any SUBDIR), leading to `make distcheck'
failure.

Fixes: d77fa310ed8 "ilo: EOL drop unmaintained gallium drv from buildsys"
Signed-off-by: Emil Velikov <f20878473f414da183da19ee25c8722cc1d711e4@collabora.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler