SimpleCaptcha: Move the equals sign inside the <label/>

The old style does not cooperate well with the new pretty forms in
core MediaWiki, and arguably this should be done like this anyway.

Bug: 63606
Change-Id: Ifbe41ee5787bd4ed9e6144c06cd1d16f72354061
(cherry picked from commit 0f1be66bd3b85e2b4ee866d22711ec118de3ef39)