build: make clean removes .gcda and .gcno files from fuzz directory

With this commit, make clean now removes coverage files from the
fuzzing directory. Without this, subsequent fuzzing runs would have
garbled coverage signals for files in the fuzz directory as
they were never deleted with make clean.

Author: Crypt-iQ

src/Makefile.test.include

@@ -1208,7 +1208,7 @@ nodist_test_test_bitcoin_SOURCES = $(GENERATED_TEST_FILES)
 
 $(BITCOIN_TESTS): $(GENERATED_TEST_FILES)
 
-CLEAN_BITCOIN_TEST = test/*.gcda test/*.gcno $(GENERATED_TEST_FILES) $(BITCOIN_TESTS:=.log)
+CLEAN_BITCOIN_TEST = test/*.gcda test/*.gcno test/fuzz/*.gcda test/fuzz/*.gcno $(GENERATED_TEST_FILES) $(BITCOIN_TESTS:=.log)
 
 CLEANFILES += $(CLEAN_BITCOIN_TEST)