Exposure IOP: disable Deflicker for 1.6 release

It is not fully ready.

The exact problem: calculated exposure compensation for same params
(target level and percentile) differs between my deflicker implementation
and "reference implementation" (ML deflick.mo)

Fix *will* alter computation results(computed exposure), and that is accepteble
only for something that was not released yet.

This does not break old (1.5) history stacks.

!!! TO BE REVERTED ONCE 1.6 IS RELEASED !!!