util/piglit-util-gl: Memory leaks in a number of tests
Memory has been allocated but never freed, which causes memory leaks in a number of tests:
arb_point_sprite-mipmap glsl-fs-bug25902 glsl-fs-sampler-numbering tex-border-1 gl-2.0-link-empty-prog arb_point_sprite-checkerboard
Fixes: 3def81d0 (Unify piglit_checkerboard_texture between GL and GLES) Signed-off-by: Yevhenii Kolesnikov yevhenii.kolesnikov@globallogic.com