Remove line breaks within t() strings

From #2454215: YouTube JavaScript Player API Deprecated #7:

@guschilds, be careful that strings run through t() don't end up with line breaks in them, otherwise those line-breaks will cause problems with translations.

There are several instances in this commit of strings in t() (usually form item descriptions) getting line-breaks added at the 80 character mark. Maybe your editor needs a Drupal plugin? :)

Reopening for a follow-up commit.

edit: it looks like the text #markup element could use that fix too! (that one was likely my fault)

This affects both 8.x and 7.x and patches need to be created for both.