Remove SMW dirty hack from Dockerfile (#578)

With the unified composer autoloader, wfLoadExtension('SemanticMediaWiki')
works properly. The sed hack that replaced it with enableSemantics() in
installedExtensions.txt is no longer needed.

Author: cicalese

Dockerfile

@@ -13,10 +13,6 @@ RUN php /tmp/extensions-skins.php "/tmp/contents.yaml"
 ENV MW_MAINTENANCE_CIRRUSSEARCH_UPDATECONFIG=2 \
 	MW_MAINTENANCE_CIRRUSSEARCH_FORCEINDEX=2
 
-# Dirty hack for Semantic MediaWiki
-RUN set -x; \
-	sed -i "s/#wfLoadExtension('SemanticMediaWiki');/#enableSemantics('localhost');/g" $MW_ORIGIN_FILES/installedExtensions.txt
-
 # Maintenance scripts for specific extensions
 COPY cirrus-search-maintenance.sh _sources/scripts/maintenance-scripts/
 COPY getSMWSettings.php _sources/canasta/