Revert "bitbake.conf: Add all layers (from BBLAYERS) to PSEUDO_IGNORE_PATHS"

This reverts commit cc30537b.

There are issues with this change where the build directory may be included
within the paths included in BBLAYERS, which is particularly problematic
where people are using kas.

An alternative to this to handle the pyc file issue is being worked on but
revert this for now whilst that fix is developed.