Disable tile data pool

It looks like at least in some circumstances it can make rendering of
the image 5-30% slower. I will disable it by default until further
details are investigated.

If you modified your performance settings, this auto-disabling will
not work. You should disable it manually by setting its size to 0%
in Preferences->Performace tab.

The testing, where the slowdown was registered, was done on 4k
image using KisProjectionBenchmark.

CC:kimageshop@kde.org