qcolordialog_mac.mm, qfiledialog_mac.mm, qfontdialog_mac.mm, and
qnspanelproxy_mac.mm are unused, remove them. The functionality they
used to provide is already included in the Cocoa platform plugin.

Change-Id: I2815d119687fd8d8dd421da36563afbd645ee000
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>