Replace RemoveWithoutPathExpansion(.*, nullptr) with Value::RemoveKey()

DictionaryValue::RemoveWithoutPathExpansion() is deprecated. For the
case where nullptr is passed for the output argument, Value::RemoveKey()
is a trivial replacement.

Mostly done with the following command line, plus a bit of finesse:
% git grep -l RemoveWithoutPathExpansion | \
  xargs sed -E -i 's/RemoveWithoutPathExpansion\((.*), nullptr/RemoveKey\(\1/g'

Bug: 646113

This CL was uploaded by git cl split.

R=jdoerrie@chromium.org

Change-Id: I5b949189dc4a977897dc31bbb36df8fedd1e2e08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298780
Auto-Submit: Anand K Mistry <amistry@chromium.org>
Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788529}

base/values.cc

@@ -1571,7 +1571,7 @@ bool DictionaryValue::RemovePath(StringPiece path,
   result = subdict->RemovePath(path.substr(delimiter_position + 1),
                                out_value);
   if (result && subdict->empty())
-    RemoveWithoutPathExpansion(subdict_path, nullptr);
+    RemoveKey(subdict_path);
 
   return result;
 }