Remove yacc output files in clean, not distclean

libsql yacc output files are generated by make, not configure.
So they should be removed by clean, not distclean.

src/sql/Makefile.am

@@ -1,11 +1,8 @@
 lib_LTLIBRARIES	=	libmdbsql.la
 libmdbsql_la_SOURCES=	mdbsql.c parser.y lexer.l 
 libmdbsql_la_LDFLAGS = -version-info 2:0:0 -Wl,--version-script=$(srcdir)/libmdbsql.map
-DISTCLEANFILES = parser.c parser.h lexer.c
+CLEANFILES = parser.c parser.h lexer.c
 AM_CPPFLAGS	=	-I$(top_srcdir)/include $(GLIB_CFLAGS)
 LIBS	=	$(GLIB_LIBS)
 libmdbsql_la_LIBADD =	../libmdb/libmdb.la
 YACC = @YACC@ -d
-
-dist-hook:
-	rm -f $(distdir)/parser.c $(distdir)/parser.h $(distdir)/lexer.c