Minor: Remove unneeded include from qquickitem.h

Clean up after 0cb12e9e01b8309320706fab219945f0ff159413

Change-Id: I7e7f0c1f7e3b9bb994bc8fd50e1c9ba462e99e28
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>