MacVim Makefile don't make macvim-dmg depend on macvim

This makes it easier to build custom DMG files from aribitrary app
bundles. For example, this is necessary for signing an existing MacVim
app and re-bundling it to DMG. Otherwise the make command will always
override the provided app bundle.

src/Makefile

@@ -3417,7 +3417,7 @@ DMGFILE = MacVim.dmg
 macvim: $(VIMTARGET)
 	xcodebuild -project MacVim/MacVim.xcodeproj $(XCODEFLAGS)
 
-macvim-dmg: macvim
+macvim-dmg:
 	mkdir -p $(DMGDIR)
 	cp -a $(RELEASEDIR)/MacVim.app $(DMGDIR)/
 	rm -rf $(RELEASEDIR)/$(DMGFILE)