Make the LGTM field not required when publishing comments

We already default it to abstain if it was not supplied in the
form post data.  So there is no reason to require that the user
supply it to us.

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

webapp/codereview/views.py

@@ -1076,7 +1076,7 @@ class PublishCommentsForm(BaseForm):
                             max_length=10000,
                             widget=forms.Textarea(attrs={'cols': 60}))
 
-  lgtm = forms.CharField(label='Code review')
+  lgtm = forms.CharField(required=False, label='Code review')
   verified = forms.BooleanField(required=False,
                                 label='Verified')