Don't install uwsgi for keystone

This is already unconditionally installed via install_apache_uwsgi in
stack.sh; we don't need to install it again in keystone.  Since we
need workarounds on some platforms (see
I3bc5260e77cebe852cc8d70d9eddf84ef71d74bb) we only want to do this in
one place.

Change-Id: I40d84cbdf68cf6bb5cba143b6c0c126cdb8a84d4

lib/keystone

@@ -504,8 +504,6 @@ function install_keystone {
 
     if [ "$KEYSTONE_DEPLOY" == "mod_wsgi" ]; then
         install_apache_wsgi
-    elif [ "$KEYSTONE_DEPLOY" == "uwsgi" ]; then
-        pip_install uwsgi
     fi
 }