Remove unused parsing support for <require commit=""/>

We haven't supported this in a while, but the parser was still here.
Its all dead code, so strip it out.

Signed-off-by: Shawn O. Pearce <sop@google.com>

manifest.py

@@ -307,11 +307,6 @@ class Manifest(object):
                fetch=fetch,
                review=review,
                projectName=projectName)
-
-    for n in node.childNodes:
-      if n.nodeName == 'require':
-        r.requiredCommits.append(self._reqatt(n, 'commit'))
-
     return r
 
   def _ParseDefault(self, node):

remote.py

@@ -22,4 +22,3 @@ class Remote(object):
     self.fetchUrl = fetch
     self.reviewUrl = review
     self.projectName = projectName
-    self.requiredCommits = []