chgserver: use tryunlink

bookmarks: use tryunlink

shelve: use tryunlink

vfs: add tryunlink method Thoughout hg code, we see a pattern of attempting to remove a file and then catching and ignoring any errors due to a missing file in the calling code. Let's unify this pattern in a single implementation in the vfs layer.

util: use tryunlink in unlinkpath We just introduced a func to attempt a file removal. Start using it.

util: add tryunlink function Throughout mercurial cdoe, there is a common pattern of attempting to remove a file and ignoring ENOENT errors. Let's move this into a common function to allow for cleaner code.