remotefilelog: remove strkwargs() The previous commit activated previously unused code paths on Python 3 and revealed that we were calling strkwargs() on a dict that already had str keys. The only caller of _forceprefetch() is _adjustlinknode() a few lines up and the static commonlogkwargs dict features str keys. Differential Revision: https://phab.mercurial-scm.org/D5958