libbpf: cleanup Makefile, remove unused elements

The plugin_dir_SQ variable is not used, remove it.
The function update_dir is also unused, remove it.
The variable $VERSION_FILES is empty, remove it.

These all originates from the introduction of the Makefile, and is likely a copy paste
from tools/lib/traceevent/Makefile.

Fixes: 1b76c13e4b ("bpf tools: Introduce 'bpf' library and add bpf feature check")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/Makefile

@@ -93,7 +93,6 @@ export prefix libdir src obj
 # Shell quotes
 libdir_SQ = $(subst ','\'',$(libdir))
 libdir_relative_SQ = $(subst ','\'',$(libdir_relative))
-plugin_dir_SQ = $(subst ','\'',$(plugin_dir))
 
 LIB_FILE = libbpf.a libbpf.so
 
@@ -150,7 +149,7 @@ CMD_TARGETS = $(LIB_FILE)
 
 TARGETS = $(CMD_TARGETS)
 
-all: fixdep $(VERSION_FILES) all_cmd
+all: fixdep all_cmd
 
 all_cmd: $(CMD_TARGETS)
 
@@ -169,16 +168,6 @@ $(OUTPUT)libbpf.so: $(BPF_IN)
 $(OUTPUT)libbpf.a: $(BPF_IN)
 	$(QUIET_LINK)$(RM) $@; $(AR) rcs $@ $^
 
-define update_dir
-  (echo $1 > $@.tmp;				\
-   if [ -r $@ ] && cmp -s $@ $@.tmp; then	\
-     rm -f $@.tmp;				\
-   else						\
-     echo '  UPDATE                 $@';	\
-     mv -f $@.tmp $@;				\
-   fi);
-endef
-
 define do_install
 	if [ ! -d '$(DESTDIR_SQ)$2' ]; then		\
 		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$2';	\
@@ -204,7 +193,7 @@ config-clean:
 	$(Q)$(MAKE) -C $(srctree)/tools/build/feature/ clean >/dev/null
 
 clean:
-	$(call QUIET_CLEAN, libbpf) $(RM) *.o *~ $(TARGETS) *.a *.so $(VERSION_FILES) .*.d .*.cmd \
+	$(call QUIET_CLEAN, libbpf) $(RM) *.o *~ $(TARGETS) *.a *.so .*.d .*.cmd \
 		$(RM) LIBBPF-CFLAGS
 	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf