[Beignet] Copyright problems in test suite

[Rebecca N. Palmer]

kernels/compiler_mandelbrot.cl kernels/compiler_mandelbrot_alternate.cl 
kernels/compiler_mandelbrot_alternate_ref.bmp 
kernels/compiler_mandelbrot_ref.bmp were included in my previous report 
by mistake: they are not actually part of the Shadertoy set, so can be kept.

To keep the test suite runnable after removing the others, 
compiler_shader_toy.cpp needs to be removed from the list in 
utests/CMakeLists.txt (and probably deleted, as it's useless without any 
kernels to run).