glapi: Do not use glapidispatch.h.

glapi: Do not use glapidispatch.h.

glapidispatch.h exists so that core mesa (libmesa.a) can be built for
DRI drivers or for non-DRI drivers as a compile time decision (whether
IN_DRI_DRIVER is defined).  It is of no use to glapi.  This commit also
drops the use of glapidispatch.h in glx and libgl-xlib as they are
considered extensions to glapi when it comes to defining public GL
entries.