Don't compile the static OpenCL kernels while loading a spreadsheet

It has the potential to slow down the loading as we wait for the
compilation thread to finish when loading has otherwise
finished. Besides, the static kernels are not even used any more.

Keep the static kernel source code and the code that handles it for
now, for reference. Also keep the compilation thread source for future
modifications and re-use.

Change-Id: I7ae6ad08b0ac00a15cc4ce5bc9906972e7e23850
A bit more informative logging (temporary)

Change-Id: I2b8bfad0d39e7c7ab059d58db54bcc2136bd9ce2
We don't use the static OpenCL kernels any more

So remove them and code related only to them.

Change-Id: Ibd09e7a801b9757443b6f87018570ec007e201d5