Remove unused target --- compactor_test

Summary:
Remove compactor_test, which depends on a directory not exist
in our code base.
    make compactor_test
    GEN      util/build_version.cc
    GEN      util/build_version.cc
    make: *** No rule to make target `utilities/compaction/compactor_test.o', needed by `compactor_test'.  Stop.

Test Plan: verify the output message of make compactor_test

Reviewers: rven, anthony, kradhakrishnan, igor, IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D40341

Makefile

@@ -806,9 +806,6 @@ listener_test: db/listener_test.o $(LIBOBJECTS) $(TESTHARNESS)
 thread_list_test: util/thread_list_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
-compactor_test: utilities/compaction/compactor_test.o $(LIBOBJECTS) $(TESTHARNESS)
-	$(AM_LINK)
-
 compact_files_test: db/compact_files_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)