remove pointless LIBS path

QT+=multimedia handles that already.

Change-Id: Ifc3be513be10d89de3ea03f11f9d41d7d56d432b
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/imports/multimedia/multimedia.pro

 QT += qml quick network multimedia-private qtmultimediaquicktools-private
 
-LIBS += -L$$QT.multimedia.libs
-
 HEADERS += \
         qdeclarativeaudio_p.h \
         qdeclarativemediametadata_p.h \