Remove _MergeMasters

This was added in https://codereview.chromium.org/178223016 and used
for rietveld which is no longer used.

Change-Id: Idbfdb50a61dba884f5212c1de904f83324a449f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5254600
Auto-Submit: Gavin Mak <gavinmak@google.com>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>

presubmit_support.py

@@ -1508,17 +1508,6 @@ class GetPostUploadExecuter(object):
         return post_upload_hook(self.gerrit, self.change, OutputApi(False))
 
 
-def _MergeMasters(masters1, masters2):
-    """Merges two master maps. Merges also the tests of each builder."""
-    result = {}
-    for (master, builders) in itertools.chain(masters1.items(),
-                                              masters2.items()):
-        new_builders = result.setdefault(master, {})
-        for (builder, tests) in builders.items():
-            new_builders.setdefault(builder, set([])).update(tests)
-    return result
-
-
 def DoPostUploadExecuter(change, gerrit_obj, verbose):
     """Execute the post upload hook.
 

tests/presubmit_unittest.py

@@ -904,47 +904,6 @@ def CheckChangeOnCommit(input_api, output_api):
                                 patchset=0,
                                 author=None)
 
-    def testMergeMasters(self):
-        merge = presubmit._MergeMasters
-        self.assertEqual({}, merge({}, {}))
-        self.assertEqual({'m1': {}}, merge({}, {'m1': {}}))
-        self.assertEqual({'m1': {}}, merge({'m1': {}}, {}))
-        parts = [
-            {
-                'try1.cr': {
-                    'win': set(['defaulttests'])
-                }
-            },
-            {
-                'try1.cr': {
-                    'linux1': set(['test1'])
-                },
-                'try2.cr': {
-                    'linux2': set(['defaulttests'])
-                }
-            },
-            {
-                'try1.cr': {
-                    'mac1': set(['defaulttests']),
-                    'mac2': set(['test1', 'test2']),
-                    'linux1': set(['defaulttests'])
-                }
-            },
-        ]
-        expected = {
-            'try1.cr': {
-                'win': set(['defaulttests']),
-                'linux1': set(['defaulttests', 'test1']),
-                'mac1': set(['defaulttests']),
-                'mac2': set(['test1', 'test2'])
-            },
-            'try2.cr': {
-                'linux2': set(['defaulttests'])
-            },
-        }
-        for permutation in itertools.permutations(parts):
-            self.assertEqual(expected, functools.reduce(merge, permutation, {}))
-
     def testMainPostUpload(self):
         os.path.isfile.side_effect = lambda f: 'PRESUBMIT.py' in f
         os.listdir.return_value = ['PRESUBMIT.py']