Fix bug PYSIDE-172: multiple rules for file

Remove moc_qpytextobject.cxx from the list of Shiboken-generated files,
as it is properly generated by MOC, and being in both places causes some
generators (e.g. Ninja) to be unhappy about having multiple rules that
(claim to) generate it.

Change-Id: I2458502852f792661120f561a59ad9a198286005
Reviewed-by: John Ehresman <jpe@wingware.com>