Handle the case when non-optional props have the same value

foo=true
foo=true
foo?=false

Consider the above case: Then the duplication of foo is allowed because
they have the same value (true). However, there was a bug that the
optional assirgnment foo?=false is left unmodified.

This fixes the bug by commenting such optional assignments.

Exempt-From-Owner-Approval: fixes a broken build

Bug: 117892318
Bug: 158735147
Test: atest test_post_process_props
Test: m out/target/product/vsoc_x86/vendor/build.prop for  cf_x86_auto
Change-Id: Iba9b61d9779d93e86d9bead2286f945f8d51ab1d

tools/post_process_props.py

@@ -88,6 +88,8 @@ def override_optional_props(prop_list, allow_dup=False):
     if len(overriding_props) > 1:
       # duplicated props are allowed when the all have the same value
       if all(overriding_props[0].value == p.value for p in overriding_props):
+        for p in optional_props:
+          p.delete("overridden by %s" % str(overriding_props[0]))
         continue
       # or if dup is explicitly allowed for compat reason
       if allow_dup:

tools/test_post_process_props.py

@@ -221,11 +221,17 @@ class PropListTestcase(unittest.TestCase):
       stderr_redirect = io.StringIO()
       with contextlib.redirect_stderr(stderr_redirect):
         props = PropList("hello")
+        optional_prop = props.get_props("foo")[2] # the last foo?=false one
 
         # we have duplicated foo=true and foo=true, but that's allowed
         # since they have the same value
         self.assertTrue(override_optional_props(props))
 
+        # foo?=false should be commented out
+        self.assertEqual("# Removed by post_process_props.py because " +
+                         "overridden by foo=true\n#foo?=false",
+                         str(optional_prop))
+
   def test_allowDuplicates(self):
     content = """
     # comment