Remove some metrics parsing code from Core Text

Remove some metrics parsing code from Core Text

The respective value in some of the default fonts like Lucida Grande
are simply not reliable. It seems that the only reliable way to get
such information is by going through all the glyphs.

It seems that these code are not well tested on Mac and should be
removed for now since it caused visible regressions in QLineEdit
rendering.

Reviewed-by: Eskil
(cherry picked from commit 8032d6f4ced50837e126f28c1475ad89eaf91ad7)

Change-Id: I85e71a2e3228a367659be9f5f6ec3e667e0ce902
Reviewed-on: http://codereview.qt.nokia.com/1264
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jiang Jiang <jiang.jiang@nokia.com>