util: Remove extra definition of piglit_automatic.
This patch fixes this build error with GCC 10.
/usr/bin/ld: CMakeFiles/piglitutil_gl.dir/piglit-glx-util.c.o:(.bss+0x0): multiple definition of `piglit_automatic'; CMakeFiles/piglitutil_gl.dir/piglit-framework-gl.c.o:(.bss+0x14): first defined here
Signed-off-by: Vinson Lee vlee@freedesktop.org