Cannot delete a remote with multiple fetch refspecs

Steps to reproduce:

>>> import pygit2
>>> repo = pygit2.init_repository(".")
>>> repo.remotes.create("origin", "https://github.com/libgit2/pygit2.git")
>>> repo.remotes.add_fetch("origin", "refs/heads/master:refs/remotes/origin/master")
>>> repo.remotes.add_fetch("origin", "refs/tags/*:refs/tags/*")
>>> repo.remotes.delete("origin")
_pygit2.GitError, entry is not unique due to being a multivar

This is present in the latest release and I also saw it happen (though with different error text) in 0.27

There doesn't appear to be a viable workaround because the libgit2 function for deleting multivars in the config isn't exposed in pygit2. Otherwise I would have tried to remove the multiple fetch entries directly ahead of time and then delete the remote.

首先复现提供的 pygit2 代码片段，并检查 pygit2 暴露的远程仓库删除和配置处理。删除具有多个 fetch refspec 的远程仓库时能够成功且不出现 multivar 错误，并有一个覆盖该示例的回归测试后，修复才算完成。