[1.6.x] Updated the `databases` documentation

 + Removed a reference about MySQL storage engines also being
   called 'table types', as this term has been deprecated for
   8 years and is no longer used.

 + Fixed the link to the official InnoDB storage engine docs.

 + Apache (versions >= 2.4) will always choose a multi-threaded
   MPM module on modern operating systems (later than 2002).

Backport of fa217d14a0 from master