CMake: HAVE_MESA isn't really a thing anymore

dtool/Config.cmake

@@ -644,38 +644,6 @@ version and below, which may reduce runtime portability to other
 systems, but it will avoid issues with getting extension function
 pointers.")
 
-# Is Mesa installed separately from OpenGL?  Mesa is an open-source
-# software-only OpenGL renderer.  Panda can link with it
-# independently from OpenGL (and if Mesa is built statically, and/or
-# with -DUSE_MGL_NAMESPACE declared to rename gl* to mgl*, it can
-# switch between the system OpenGL implementation and the Mesa
-# implementation at runtime).
-
-# Also, Mesa includes some core libraries (in libOSMesa.so) that
-# allow totally headless rendering, handy if you want to run a
-# renderer as a batch service, and you don't want to insist that a
-# user be logged on to the desktop or otherwise deal with X11 or
-# Windows.
-
-# TODO: Mesa
-#find_package(Mesa)
-
-#package_option(MESA
-#  "When set, will build libmesadisplay, which can be used in lieu of
-#libpandagl or libpandadx to do rendering.  However, for most
-#applications, you don't need to do this, since (a) if you have
-#hardware rendering capability, you probably don't want to use Mesa,
-#since it's software-only, and (b) if you don't have hardware
-#rendering, you can install Mesa as the system's OpenGL
-#implementation, so you can just use the normal libpandagl.
-#You only need to define HAVE_MESA if you want to run totally headless,
-#or if you want to be able to easily switch between Mesa and the
-#system OpenGL implementation at runtime.  If you compiled Mesa with
-#USE_MGL_NAMESPACE defined, define MESA_MGL here.")
-
-set(MIN_MESA_VERSION "1 1" CACHE STRING
-  "Similar to MIN_GL_VERSION, above.")
-
 
 # Should build tinydisplay?
 option(HAVE_TINYDISPLAY