contrib: restore the `hg fix` configuration in the examples After decc3bd3f20d, running `black` will DTRT, but running `hg fix` did nothing (unless the example config file was %included, in which case it truncated the file instead of formatting it). I'm not sure why that was happening, but let's not leave a code shredder laying around. Differential Revision: https://phab.mercurial-scm.org/D10311