Remove timestamp based rebuilds (#1174)

If you want to build a package without changing the version number,
please use `--force` from now on. For example:

    pmbootstrap build --force hello-world

Prior to this commit, changes were detected automatically (timestamp
based rebuilds). However, that feature does not work as expected with
the binary package repository we have now, and depending on how you use
git, it has never worked. Close #1167, close #1156, close #1023 and
close #985. This commit also mentions --force when a package is up to date,
but the user requested to build it.

pmb/helpers/git.py

@@ -45,34 +45,3 @@ def rev_parse(args, revision="HEAD"):
         logging.warning("WARNING: Failed to determine revision of git repository at " + args.aports)
         return ""
     return rev.rstrip()
-
-
-def find_out_of_sync_files_tracked(args, git_root):
-    """
-    Find all files tracked by git, that are are out of sync with origin/HEAD.
-
-    In some cases (when you rename a remote or add it manually), origin/HEAD
-    does not exist. We check for that to provide a meaningful error message
-    instead of a confusing crash (see #151).
-    See also: <https://stackoverflow.com/a/17639471>
-    """
-    # Return changed files compared to origin/HEAD when it exists
-    ret = pmb.helpers.run.user(args, ["git", "show-ref",
-                                      "refs/remotes/origin/HEAD"],
-                               working_dir=git_root, return_stdout=True,
-                               check=False)
-    if ret and "refs/remotes/origin/HEAD" in ret:
-        return pmb.helpers.run.user(args, ["git", "diff", "--name-only",
-                                           "origin"], working_dir=git_root,
-                                    return_stdout=True)
-
-    # Meaningful error
-    logging.debug("Output of 'git diff --name-only origin': " + str(ret))
-    logging.info("See also: <https://github.com/postmarketOS/pmbootstrap/"
-                 "issues/151>")
-    fix_cmds = ("git symbolic-ref refs/remotes/origin/HEAD refs/remotes/"
-                "origin/master; git fetch")
-    raise RuntimeError("Your aports repository does not have the"
-                       " 'origin/HEAD' reference. Please add it by"
-                       " running the following commands inside " +
-                       git_root + ": " + fix_cmds)