JavaScriptMinifier: Remove support for unused $statementsOnOwnLine flag

JavaScriptMinifier: Remove support for unused $statementsOnOwnLine flag

The $wgResourceLoaderMinifierStatementsOnOwnLine config var was deprecated
in MediaWiki 1.27. The parameter of minify() was not used by other code, and
no new usage has been introduced since then, either.

Remove the feature from JavaScriptMinifier, and add a release note for that.
The same 1.31 release notes also contain a note already about the removal
of the configuration variable.

The feature was not covered by unit tests.

The following private variables have been removed, that are no longer used
due to this change: $newlineBefore, $newlineAfter, $newlineAdded.

Change-Id: I2cbf271156c1954abb982531d0125b4b9573b12c