tidy: codify unnecessary else policy

[reidpr]

Split from #1860. Pylint:

• R1705 no-else-return
• R1723 no-else-break

charliecloud/lib/build_cache.py

Lines 388 to 397 in d679373

	if ((fm.st.st_dev, fm.st.st_ino) in hardlinks):
	ch.DEBUG("hard link: deleting subsequent: %d %d %s"
	% (fm.st.st_dev, fm.st.st_ino, path))
	fm.hardlink_to = hardlinks[(fm.st.st_dev, fm.st.st_ino)]
	fm.path_abs.unlink()
	return fm
	else:
	ch.DEBUG("hard link: recording first: %d %d %s"
	% (fm.st.st_dev, fm.st.st_ino, path))
	hardlinks[(fm.st.st_dev, fm.st.st_ino)] = path

The else is indeed redundant, though I recall putting it there on purpose, probably thinking it was clearer. But we should probably be consistent, and it seems prohibitively difficult to positively enforce using else in these cases.