Ignore css in displaytitle when $wgRestrictDisplayTitle is enabled
DISPLAYTITLE restrictions can be abused with css declarations such as font-size:0 , similar to display=none as was reported in T28547.
Propose disallowing all css declarations from the wikitext in to titles when $wgRestrictDisplayTitle is enabled
See also report on enwiki from user:InvalidOS here: https://en.wikipedia.org/w/index.php?title=Wikipedia:Administrators%27_noticeboard&oldid=894118189#Exploit_in_the_DISPLAYTITLE_behavior_switch_involving_html_tags