android: drop no longer working make target (#14673)

Leftover from 2019, the `dev` target was removed in koreader/android-luajit-launcher@0bd2f4b.

make/android.mk

@@ -38,7 +38,7 @@ endif
 
 # Update. {{{
 
-PHONY += androiddev update
+PHONY += update
 
 ANDROID_DIR = $(PLATFORM_DIR)/android
 ANDROID_LAUNCHER_DIR = $(ANDROID_DIR)/luajit-launcher
@@ -85,9 +85,6 @@ LICENSE*
 NOTICE
 endef
 
-androiddev: update
-	$(MAKE) -C $(ANDROID_LAUNCHER_DIR) dev
-
 update: all
 	# Note: do not remove the module directory so there's no need
 	# for `mk7z.sh` to always recreate `koreader.7z` from scratch.