Revert "BAC-1049: Enable Swift on new wikis by default"

This reverts commit 861cf3a1f92fdf0685122e4c1c9eee923aeaa7af.

Revert #2062 / backport #2532
Merge pull request #2617 from Wikia/release-206-bac-1209

Do not enable Swift on new wikis by default (release-206)