Remove regex usage from places that don't need it

In revwalk, we are doing a very simple check to see if a string
contains wildcard characters, so a full regular expression match
is not needed.

In remote listing, now that we have git_config_foreach_match with
full regular expression matching, we can take advantage of that
and eliminate the regex here, replacing it with much simpler string
manipulation.
Merge pull request #1864 from libgit2/minimize-regex-usage

Minimize regex usage