make file removal a bit more robust

Some of the file removal calls are subject to race conditions (if
something else deletes the file), so extend our remove API to have
an option to ignore ENOENT errors.  Then update a bunch of random
call sites to use this new functionality.

Change-Id: I31a9090e135452033135337a202a4fc2dbf8b63c
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/319195
Reviewed-by: Sean McAllister <smcallis@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

git_config.py

@@ -352,8 +352,8 @@ class GitConfig(object):
       Trace(': parsing %s', self.file)
       with open(self._json) as fd:
         return json.load(fd)
-    except (IOError, ValueError):
-      platform_utils.remove(self._json)
+    except (IOError, ValueErrorl):
+      platform_utils.remove(self._json, missing_ok=True)
       return None
 
   def _SaveJson(self, cache):
@@ -361,8 +361,7 @@ class GitConfig(object):
       with open(self._json, 'w') as fd:
         json.dump(cache, fd, indent=2)
     except (IOError, TypeError):
-      if os.path.exists(self._json):
-        platform_utils.remove(self._json)
+      platform_utils.remove(self._json, missing_ok=True)
 
   def _ReadGit(self):
     """