Move dependency on user.tokens from mediawiki.api.edit to mediawiki.api

Move dependency on user.tokens from mediawiki.api.edit to mediawiki.api

The postWithToken() method used to be specific to the edit module.
However that logic was moved and refactored into getToken() and
postWithToken() a while back.

While waiting for user.tokens instead of making api requests for tokens
is worth it. The logic in mediawiki.api.js inspects mw.user.tokens
only at initial run time. So it must be on 'mediawiki.api'.

Anyhow, in practice it doesn't matter since the user.tokens is
embedded in the page. So there's no actual waiting of any kind.

Change-Id: I10fae93c8f1500b4aa752101256fbba94c2ae40d