compositor: Fix GL without ARB_texture_rectangle

Bug 11962

The compositor using GL for tear-free rendering would generate corrupted
output on some older nv34 card because it wrongly uses GL_TEXTURE_2D
instead of GL_TEXTURE_RECTANGLE_ARB which is supported on this hardware.

Remove detection of "GL_ARB_texture_rectangle" and
"GL_ARB_texture_non_power_of_two" which are GL extensions, not GLX.

Instead, rely on GLX_BIND_TO_TEXTURE_TARGETS_EXT returned values to
determine the texture type and target to use.

See also: https://bugs.freedesktop.org/show_bug.cgi?id=90871


Thanks to Hans de Goede <jwrdegoede@fedoraproject.org> and Ilia Mirkin
<imirkin@alum.mit.edu> for their help on this issue.

Signed-off-by: Olivier Fourdan <fourdan@xfce.org>