samples/bpf: Drop unnecessarily inclusion for bpf_load

Drop inclusion for bpf_load -I$(objtree)/usr/include as it is
included for all objects anyway, with above line:
KBUILD_HOSTCFLAGS += -I$(objtree)/usr/include

Signed-off-by: Ivan Khoronzhuk <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

samples/bpf/Makefile

···
 KBUILD_HOSTCFLAGS += -I$(srctree)/tools/lib/ -I$(srctree)/tools/include
 KBUILD_HOSTCFLAGS += -I$(srctree)/tools/perf
 
-HOSTCFLAGS_bpf_load.o += -I$(objtree)/usr/include -Wno-unused-variable
+HOSTCFLAGS_bpf_load.o += -Wno-unused-variable
 
 KBUILD_HOSTLDLIBS		+= $(LIBBPF) -lelf
 HOSTLDLIBS_tracex4		+= -lrt