Rename functions "util.Remove" (remove.go) to "util.RemoveWithRetry"
(file_retry.go) and add comments to clarify their behaviors, also add
tests.
Refactor callers: when no concurrent access (cmd cli, migration, app
init, test), use "os.Xxx" directly.
More details are in `modules/util/file_retry.go`
By the way, clean up OS (windows) detection, make FileURLToPath test
always run
before: gitrepo vs git packages
after: git package fully handle all git operations
by the way, use `WithRepo(repo)` instead of `WithDir(repo.Path)` to hide
path details.
benefits:
1. remove all unnecessary wrappers, developers no need to struggle with
"which package should be used"
2. simplify code, RepositoryFacade can (will) be used everywhere, all
"path" details are (will be) hidden
