Remove pystache in favor of our custom version

repo-requirements.txt

 -e git://github.com/MITx/django-staticfiles.git@6d2504e5c8#egg=django-staticfiles
 -e git://github.com/MITx/django-pipeline.git#egg=django-pipeline
 -e git://github.com/benjaoming/django-wiki.git@c145596#egg=django-wiki
+-e git://github.com/dementrock/pystache_custom.git#egg=pystache_custom
 -e common/lib/capa
 -e common/lib/xmodule

requirements.txt

@@ -43,5 +43,4 @@ django-storages
 django-threaded-multihost
 django-sekizai<0.7
 networkx
-pystache>=0.5.2
 -r repo-requirements.txt