Remote refspecs minor fixes

Remote ```git_remote_pushspec```, it's a leftover from #1493.

I'm a bit worried that there were no compilation warnings about this.

The test fix confused me. The test in question doesn't fail in travis but fails locally with:
```
1:   1) Failure:
1: clone::nonetwork::custom_fetch_spec [/Users/nvloff/projects/nvloff/libgit2/tests-clar/clone/nonetwork.c:153]
1:   String mismatch: "refs/heads/master" != git_refspec_src(actual_fs)
1:   'refs/heads/master' != 'refs/heads/*'
```