qt5base: Remove feature test for posix_fallocate in sqlite code

It's already checked by the build system more accurately.

Fixes:

  http://autobuild.buildroot.net/results/e3b/e3b26ee314880fdb50bb774a0539bfba04d9fbcf/



Signed-off-by: Fatih Aşıcı <fatih.asici@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>