Mac Style: Fix QLineEdit frame in 10.10

Also removes some dead code.

Backport of 83f06da1c6bffff61af78cbe75a0691d53742b53 from qt5/qtbase

Change-Id: I7e088ca8b52bc3e2da25e29ab570469eab6f97bf
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>