pkgconfig.bbclass: also remove -isystem flag
pkgconfig.bbclass: also remove -isystem flag

First seen in libclamav.pc, may be relevant for other packages too

Signed-off-by: Roman I Khimov <9c65a1c4e83e5c30b8a170f663f3fbf79112fbfa@altell.ru>

rascalmicro/openembedded-rascal,SIFTeam/openembedded,sampov2/audio-openembedded,SIFTeam/openembedded,anguslees/openembedded-android,buglabs/oe-buglabs,yyli/overo-oe,giobauermeister/openembedded,rascalmicro/openembedded-rascal,JamesAng/oe,sentient-energy/emsw-oe-mirror,nx111/openembeded_openpli2.1_nx111,Martix/Eonos,openembedded/openembedded,thebohemian/openembedded,BlackPole/bp-openembedded,SIFTeam/openembedded,mrchapp/arago-oe-dev,giobauermeister/openembedded,sentient-energy/emsw-oe-mirror,thebohemian/openembedded,giobauermeister/openembedded,dellysunnymtech/sakoman-oe,BlackPole/bp-openembedded,libo/openembedded,sampov2/audio-openembedded,John-NY/overo-oe,JamesAng/goe,sledz/oe,dellysunnymtech/sakoman-oe,thebohemian/openembedded,xifengchuo/openembedded,yyli/overo-oe,mrchapp/arago-oe-dev,xifengchuo/openembedded,John-NY/overo-oe,sutajiokousagi/openembedded,dave-billin/overo-ui-moos-auv,JamesAng/goe,trini/openembedded,anguslees/openembedded-android,openembedded/openembedded,openpli-arm/openembedded,openembedded/openembedded,BlackPole/bp-openembedded,sledz/oe,nx111/openembeded_openpli2.1_nx111,hulifox008/openembedded,nx111/openembeded_openpli2.1_nx111,dave-billin/overo-ui-moos-auv,anguslees/openembedded-android,scottellis/overo-oe,openpli-arm/openembedded,sentient-energy/emsw-oe-mirror,JamesAng/goe,mrchapp/arago-oe-dev,sutajiokousagi/openembedded,John-NY/overo-oe,dave-billin/overo-ui-moos-auv,BlackPole/bp-openembedded,rascalmicro/openembedded-rascal,yyli/overo-oe,scottellis/overo-oe,dellysunnymtech/sakoman-oe,openpli-arm/openembedded,JamesAng/oe,sledz/oe,nx111/openembeded_openpli2.1_nx111,sutajiokousagi/openembedded,John-NY/overo-oe,Martix/Eonos,hulifox008/openembedded,trini/openembedded,anguslees/openembedded-android,giobauermeister/openembedded,sentient-energy/emsw-oe-mirror,scottellis/overo-oe,mrchapp/arago-oe-dev,thebohemian/openembedded,buglabs/oe-buglabs,openembedded/openembedded,dellysunnymtech/sakoman-oe,JamesAng/goe,buglabs/oe-buglabs,SIFTeam/openembedded,sutajiokousagi/openembedded,buglabs/oe-buglabs,openembedded/openembedded,sentient-energy/emsw-oe-mirror,Martix/Eonos,JamesAng/goe,nx111/openembeded_openpli2.1_nx111,Martix/Eonos,scottellis/overo-oe,xifengchuo/openembedded,openembedded/openembedded,scottellis/overo-oe,giobauermeister/openembedded,openpli-arm/openembedded,SIFTeam/openembedded,openembedded/openembedded,rascalmicro/openembedded-rascal,dellysunnymtech/sakoman-oe,openpli-arm/openembedded,buglabs/oe-buglabs,libo/openembedded,openembedded/openembedded,openembedded/openembedded,libo/openembedded,JamesAng/oe,rascalmicro/openembedded-rascal,dave-billin/overo-ui-moos-auv,dellysunnymtech/sakoman-oe,trini/openembedded,Martix/Eonos,mrchapp/arago-oe-dev,thebohemian/openembedded,buglabs/oe-buglabs,dellysunnymtech/sakoman-oe,libo/openembedded,yyli/overo-oe,John-NY/overo-oe,xifengchuo/openembedded,buglabs/oe-buglabs,libo/openembedded,openembedded/openembedded,dave-billin/overo-ui-moos-auv,BlackPole/bp-openembedded,sutajiokousagi/openembedded,sampov2/audio-openembedded,anguslees/openembedded-android,sampov2/audio-openembedded,xifengchuo/openembedded,yyli/overo-oe,mrchapp/arago-oe-dev,rascalmicro/openembedded-rascal,dellysunnymtech/sakoman-oe,mrchapp/arago-oe-dev,JamesAng/oe,rascalmicro/openembedded-rascal,scottellis/overo-oe,giobauermeister/openembedded,nx111/openembeded_openpli2.1_nx111,libo/openembedded,giobauermeister/openembedded,thebohemian/openembedded,buglabs/oe-buglabs,sampov2/audio-openembedded,yyli/overo-oe,JamesAng/oe,openpli-arm/openembedded,xifengchuo/openembedded,sampov2/audio-openembedded,sampov2/audio-openembedded,Martix/Eonos,JamesAng/goe,giobauermeister/openembedded,sledz/oe,xifengchuo/openembedded,hulifox008/openembedded,trini/openembedded,sentient-energy/emsw-oe-mirror,trini/openembedded,anguslees/openembedded-android,hulifox008/openembedded,trini/openembedded,hulifox008/openembedded,yyli/overo-oe,nx111/openembeded_openpli2.1_nx111,hulifox008/openembedded,sledz/oe,scottellis/overo-oe,libo/openembedded,xifengchuo/openembedded,hulifox008/openembedded,sutajiokousagi/openembedded,BlackPole/bp-openembedded,openembedded/openembedded,sutajiokousagi/openembedded,nx111/openembeded_openpli2.1_nx111,rascalmicro/openembedded-rascal,BlackPole/bp-openembedded,sledz/oe,SIFTeam/openembedded,dellysunnymtech/sakoman-oe,Martix/Eonos,JamesAng/oe,xifengchuo/openembedded,trini/openembedded,JamesAng/goe,yyli/overo-oe,thebohemian/openembedded,JamesAng/oe,openpli-arm/openembedded,SIFTeam/openembedded,anguslees/openembedded-android,dave-billin/overo-ui-moos-auv,sledz/oe,sentient-energy/emsw-oe-mirror,John-NY/overo-oe,dave-billin/overo-ui-moos-auv,John-NY/overo-oe,giobauermeister/openembedded