store: remove uneeded startswith('data/') checks in encodedir() and decodedir()
I don't think we will ever have anything in the store that resides inside a
directory that ends in .i or .d under store/ that we wouldn't want to have
direncoded. The files not under data/ surely don't need direncoding, but it
doesn't harm to let these few run through it. It hurts more to check whether the
thousands of other files start with 'data/'. They do anyway.
See also 810387f59696 (fixed with c31fe74a6633), which moved the direncoding
from filelog into store