erlc.mk: Remove the target touching source files

The touch(1) happens after `$(PROJECT).d` is generated. Therefore, with
the next run of make, `$(PROJECT).d` is considered obsolete and
recreated. Source files are touched again, and so on.

This makes the whole project to be rebuilt with every run of make.

core/erlc.mk

@@ -203,9 +203,6 @@ endef
 
 ebin/$(PROJECT).app:: $(ERL_FILES) $(CORE_FILES)
 	$(if $(strip $?),$(call compile_erl,$?))
-
-$(sort $(ERL_FILES) $(CORE_FILES))::
-	@touch $@
 endif
 
 clean:: clean-app