qt5: Remove *.la/*.prl fixup script

qt5: Remove *.la/*.prl fixup script

After fixing Prefix in our custom qt.conf, Qt computes and embeds the
correct sysroot prefixed pathes in all *.la and *.prl files.
So remove fixup of
- *.la files because they are generically fixed anyway
- *.prl files because occurences of absolute /usr/lib were no longer
observed

Signed-off-by: Andreas Naumann <anaumann@ultratronik.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>