graphics/glew-wayland: drop X11 dependency after b44acc9409bdn

libGL is legacy GLX entry point, so maybe missing if libglvnd and/or
mesa-libs was built without X11 support.

$ make clean all deinstall install WITHOUT=X11 -C ../libglvnd
$ make clean all
[...]

> glew-wayland-2.2.0_2 depends on shared library: libGL.so - not found

• Error code 1

[...]
ld -shared -soname libGLEW-wayland.so.2 -o lib/libGLEW-wayland.so.2.2.0 tmp/freebsd/default/shared/glew.o -L/usr/local/lib -lEGL -lGL
ld: error: unable to find library -lGL
gmake[1]: *** [Makefile:123: lib/libGLEW-wayland.so.2.2.0] Error 1