Clean up some fuzzer-related cruft.

The fuzzer can actually be built properly with Clang by overriding
`CXX`, `CXXFLAGS` and `LDFLAGS` as appropriate/desired. The "fake"
build and associated files are no longer useful if they ever were.

Change-Id: Ic47fbdac6ca6e9377fb1eb18ee12dcb2a96abc25
Reviewed-on: https://code-review.googlesource.com/c/re2/+/61970
Reviewed-by: Alex Chernyakhovsky <[email protected]>
Reviewed-by: Paul Wankadia <[email protected]>

Makefile

@@ -250,14 +250,9 @@ obj/test/regexp_benchmark: obj/libre2.a obj/re2/testing/regexp_benchmark.o $(TES
 	@mkdir -p obj/test
 	$(CXX) -o $@ obj/re2/testing/regexp_benchmark.o $(TESTOFILES) -lgtest -lbenchmark -lbenchmark_main obj/libre2.a $(RE2_LDFLAGS) $(LDFLAGS)
 
-# re2_fuzzer is a target for fuzzers like libFuzzer and AFL. This fake fuzzing
-# is simply a way to check that the target builds and then to run it against a
-# fixed set of inputs. To perform real fuzzing, refer to the documentation for
-# libFuzzer (llvm.org/docs/LibFuzzer.html) and AFL (lcamtuf.coredump.cx/afl/).
-obj/test/re2_fuzzer: CXXFLAGS:=-I./re2/fuzzing/compiler-rt/include $(CXXFLAGS)
-obj/test/re2_fuzzer: obj/libre2.a obj/re2/fuzzing/re2_fuzzer.o obj/util/fuzz.o
+obj/test/re2_fuzzer: obj/libre2.a obj/re2/fuzzing/re2_fuzzer.o
 	@mkdir -p obj/test
-	$(CXX) -o $@ obj/re2/fuzzing/re2_fuzzer.o obj/util/fuzz.o obj/libre2.a $(RE2_LDFLAGS) $(LDFLAGS)
+	$(CXX) -o $@ obj/re2/fuzzing/re2_fuzzer.o obj/libre2.a $(RE2_LDFLAGS) $(LDFLAGS)
 
 ifdef REBUILD_TABLES
 .PRECIOUS: re2/perl_groups.cc