(bug 41745) Remove ptwiki, ptwikinews from EmergencyCaptcha

This change removes ptwiki and ptwikinews from the EmergencyCaptcha
mode, for three reasons:
* (1) There has never been any community consensus to enable this
permanently;
* (2) A community discussion failed to get consensus to keep this
solution per comment 13 on bug 41745;
* (3) Our captchas are not very useful in preventing spambots anyway,
and there are better solutions (e.g. $wgRateLimits and AbuseFilter).

Change-Id: Id7b9721d9a91a30325160305b6b475ef023fd81f