make: clean up Makefile

The dependencies on the header files are handled by 'make depend'.  They
do not need to be spelled out.

usr.bin/make/Makefile

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.113 2021/02/22 20:45:46 rillig Exp $
+#	$NetBSD: Makefile,v 1.114 2021/04/11 11:41:27 rillig Exp $
 #	@(#)Makefile	5.2 (Berkeley) 12/28/90
 
 PROG=	make
@@ -23,20 +23,6 @@ SRCS+=  targ.c
 SRCS+=  trace.c
 SRCS+=  var.c
 SRCS+=  util.c
-HDRS=   buf.h
-HDRS+=  config.h
-HDRS+=  dir.h
-HDRS+=  enum.h
-HDRS+=  hash.h
-HDRS+=  job.h
-HDRS+=  lst.h
-HDRS+=  make.h
-HDRS+=  make_malloc.h
-HDRS+=  meta.h
-HDRS+=  metachar.h
-HDRS+=  nonints.h
-HDRS+=  pathnames.h
-HDRS+=  trace.h
 
 # Whether to generate a coverage report after running the tests.
 USE_COVERAGE?=	no		# works only with gcc; clang9 fails to link
@@ -128,9 +114,7 @@ SUBDIR+=	unit-tests
 .endif
 
 LINTFLAGS+=	-T	# strict bool mode, available since 2021-01-11
-
-${SRCS:M*.c:.c=.o}: ${HDRS}
-CLEANFILES+=	*.o
+CLEANFILES+=	*.o	# for filemon objects
 
 COPTS.arch.c+=	${GCC_NO_FORMAT_TRUNCATION}
 COPTS.dir.c+=	${GCC_NO_FORMAT_TRUNCATION}