android build: rm blacklist.txt

this looks like broken dead code

- the "if" body is never entered as `.buildozer/` gets created by `contrib/android/build.sh`
    8eb3c43603/contrib/android/build.sh (L32)
- `blacklist.txt` is at `contrib/android/blacklist.txt` but the Makefile expects it at the root
    ref https://gitlab.com/fdroid/fdroiddata/-/merge_requests/24948#note_2643399062
- `blacklist.txt` is not referenced anywhere else

contrib/android/Makefile

@@ -27,11 +27,6 @@ prepare:
 	# copy electrum to main.py
 	@cp buildozer_$(ELEC_APK_GUI).spec ../../buildozer.spec
 	@cp ../../run_electrum ../../main.py
-	@-if [ ! -d "../../.buildozer" ];then \
-		cd ../..; buildozer android debug;\
-		cp -f blacklist.txt .buildozer/android/platform/python-for-android/src/blacklist.txt;\
-		rm -rf ./.buildozer/android/platform/python-for-android/dist;\
-	fi
 apk:
 	@make prepare
 	@-cd ../..; buildozer android debug