qt4: replace recipes with bbappends

The only functional difference between these recipes and the ones in
oe-core is the addition of PostgreSQL, MySQL and SQLite 2 drivers. Now
that we have QT_SQL_DRIVER_FLAGS in the oe-core Qt4 recipes we can
replace the overlayed recipes with bbappends which enable the drivers
using this variable.

(Note: there is no bbappend for qt4-tools-native as this does not build
the SQL drivers.)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>