unneeded Flag Makefile in COMMON_LIBS

[konstmonst]

I couldn't build it on Arch Linux, here is the fix I had to apply:

$ git diff
diff --git a/Quake/Makefile b/Quake/Makefile
index 1d5b2fb..5f152f0 100644
--- a/Quake/Makefile
+++ b/Quake/Makefile
@@ -181,7 +181,7 @@ ifeq ($(USE_CODEC_UMX),1)
CFLAGS+= -DUSE_CODEC_UMX
endif

-COMMON_LIBS:= -lm -lGL -l:libvulkan.so.1 -lX11-xcb
+COMMON_LIBS:= -lm -l:libvulkan.so.1 -lX11-xcb

LIBS := $(COMMON_LIBS) $(NET_LIBS) $(CODECLIBS)