configure.ac: drop obsolete variable HAVE_COMMON_DRI

configure.ac: drop obsolete variable HAVE_COMMON_DRI

The original intent of the variable was to prevent adding
libdrm dependency for non drm drivers (swrast). This is
already handled with __NOT_HAVE_DRM_H, and with the recent
merge of the dri_util and drisw_util code this variable has
started causing build issues.

Eg. the following will fail
$ ./autogen.sh --with-dri-drivers=swrast --with-gallium-drivers=
$ make

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Andreas Boll <andreas.boll.dev@gmail.com>