Just use On branch ... before the initial commit

In the dashboards we already show `HEAD: No commits yet.`
so it is not necessary to special-case the branch naming
here.

core/git_mixins/active_branch.py

@@ -83,7 +83,7 @@ def _format_branch_status(self, branch_status, delim=None):
             status = "HEAD is in a detached state."
 
         elif initial:
-            status = "Initial commit on `{}`.".format(branch)
+            status = "On branch `{}`.".format(branch)
 
         else:
             tracking = " tracking `{}`".format(remote)

tests/test_repo_status.py

@@ -185,20 +185,20 @@ def test_format_branch_status_for_statusbar(self, status_lines, expected):
 ),
 (
     "## No commits yet on master",
-    "Initial commit on `master`."
+    "On branch `master`."
 ),
 (
     "## No commits yet on master\n?? foo",
-    "Initial commit on `master`."
+    "On branch `master`."
 ),
 # Previous versions of git instead emitted this before the initial commit
 (
     "## Initial commit on zoom",
-    "Initial commit on `zoom`."
+    "On branch `zoom`."
 ),
 (
     "## Initial commit on master\n?? foo",
-    "Initial commit on `master`."
+    "On branch `master`."
 ),
 ]