remove redundant statements from project files

- TARGET is unnecessary if it matches the project file's basename
- CONFIG+=no_private_qt_headers_warning is added by qt_build_config.prf
- load(qt_build_config) is done by .qmake.conf

Change-Id: I3eb45a758dfee34be3c78fc13d996780741c95e9
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>

src/plugins/avfoundation/mediaplayer/mediaplayer.pro

@@ -1,4 +1,3 @@
-load(qt_build_config)
 
 #DEFINES += QT_DEBUG_AVF
 # Avoid clash with a variable named `slots' in a Quartz header

src/plugins/gstreamer/common.pri

@@ -1,6 +1,5 @@
 
 QT += core-private multimedia-private network
-CONFIG += no_private_qt_headers_warning
 
 qtHaveModule(widgets) {
     QT += widgets multimediawidgets-private

src/plugins/qnx-audio/audio/audio.pro

@@ -1,7 +1,6 @@
 TARGET = qtmedia_qnx_audio
-QT += multimedia-private
-CONFIG += no_private_qt_headers_warning
 
+QT += multimedia-private
 
 LIBS += -lasound
 

src/plugins/resourcepolicy/resourcepolicy.pro

@@ -1,7 +1,7 @@
 TARGET = resourceqt
 
 QT += multimedia-private
-CONFIG += no_private_qt_headers_warning link_pkgconfig
+CONFIG += link_pkgconfig
 PKGCONFIG += libresourceqt5
 
 INCLUDEPATH += $$PWD \