dirstate: remove a update_file's special case for tracked file with p2 data This case was fishy and can be dealt with by passing more accurate data a higher level. This clarify the API and prepare for a larger rework of the data we feeds to the dirstate.

dirstate: deprecate `__getitem__` access If we want to drop `state` usage, we need to deprecate this. Differential Revision: https://phab.mercurial-scm.org/D11544