Revert "fixes to slow-down at jump startup and infinite air intertia growth"

This reverts commit f596b698d96a07ed4916ee056f2d4a8a00884d43.
Merge ESM::Cell fields by subrecord

Fixes an issue with the Morrowind Patched mod where cell ambient values would become black due to the new cell records not including an AMBI subrecord.

Also fixes a bug where mLeasedRefs was incorrectly cleared when overwriting a cell (*oldcell = *cell;)