omxplayer: fix compilation with GCC 6
omxplayer: fix compilation with GCC 6

Specifying -isystem${STAGING_DIR_HOST}/usr/include in INCLUDES gives:

    In file included from utils/PCMRemap.cpp:26:0:
    .../build/tmp/sysroots/raspberrypi2/usr/include/c++/6.1.1/cstdlib:75:25: fatal error: stdlib.h: No such file or directory
     #include_next <stdlib.h>
                             ^
    compilation terminated.
    Makefile:44: recipe for target 'utils/PCMRemap.o' failed

To resolve this, /usr/include shouldn't be specified as it is already a
default include path relative to the sysroot.

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70129.

Signed-off-by: Jonathan Liu <44960b6aa03eb2fb89c62409a43f0b56d13ff84f@gmail.com>

kraj/meta-raspberrypi,VCTLabs/meta-raspberrypi,VCTLabs/meta-raspberrypi,leon-anavi/meta-raspberrypi,toolmmy/meta-raspberrypi,toolmmy/meta-raspberrypi,VCTLabs/meta-raspberrypi,d21d3q/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,toolmmy/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,VCTLabs/meta-raspberrypi,schnitzeltony/meta-raspi-light,kraj/meta-raspberrypi,schnitzeltony/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,kraj/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,schnitzeltony/meta-raspberrypi,d21d3q/meta-raspberrypi,d21d3q/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,toolmmy/meta-raspberrypi,agherzan/meta-raspberrypi,d21d3q/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspi-light