Remove USE_NINJA=false

And everything special-cased on that. Add a warning if USE_NINJA is
set to let users know that it no longer changes anything.

Change-Id: Ib8739151fe26ea6bf8f76b7ac2b8f4097dab0b47
diff --git a/core/executable_prefer_symlink.mk b/core/executable_prefer_symlink.mk
index 931550f..1640b32 100644
--- a/core/executable_prefer_symlink.mk
+++ b/core/executable_prefer_symlink.mk
@@ -42,7 +42,7 @@
 # $(my_symlink) doesn't need to depend on $(PRIVATE_SRC_BINARY_NAME): we can generate symlink to nonexistent file.
 # If you add the dependency, make would compare the timestamp of a file against that of its symlink:
 # they are always equal, because make follows symlink.
-$(my_symlink): $(LOCAL_MODULE_MAKEFILE_DEP)
+$(my_symlink):
 	@echo "Symlink: $@ -> $(PRIVATE_SRC_BINARY_NAME)"
 	@mkdir -p $(dir $@)
 	@rm -rf $@