Remove unused #include from tst_api.cpp.

This fixes compilation wit Qt 4.

Change-Id: Ib3d209e51b2260e7c3f1dbe6e7acf5336e22a650
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>