samples: bpf: Cleanup bpf_load.o from Makefile

Since commit cc7f641d ("samples: bpf: Refactor BPF map performance
test with libbpf") has ommited the removal of bpf_load.o from Makefile,
this commit removes the bpf_load.o rule for targets where bpf_load.o is
not used.

Fixes: cc7f641d ("samples: bpf: Refactor BPF map performance test with libbpf")
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200823085334.9413-2-danieltimlee@gmail.com

samples/bpf/Makefile

@@ -76,7 +76,7 @@ trace_output-objs := bpf_load.o trace_output_user.o $(TRACE_HELPERS)
 lathist-objs := bpf_load.o lathist_user.o
 offwaketime-objs := bpf_load.o offwaketime_user.o $(TRACE_HELPERS)
 spintest-objs := bpf_load.o spintest_user.o $(TRACE_HELPERS)
-map_perf_test-objs := bpf_load.o map_perf_test_user.o
+map_perf_test-objs := map_perf_test_user.o
 test_overhead-objs := bpf_load.o test_overhead_user.o
 test_cgrp2_array_pin-objs := test_cgrp2_array_pin.o
 test_cgrp2_attach-objs := test_cgrp2_attach.o