chore: Only load google services if needed

Originally done in 051ec8f913 then
accidentally (?) reverted in 8a542bf5c2

android/app/build.gradle

@@ -87,4 +87,6 @@ dependencies {
     implementation "net.zetetic:android-database-sqlcipher:4.4.0" // needed for moor_ffi w/ sqlcipher
 }
 
-apply plugin: 'com.google.gms.google-services'
+if(file("google-services.json").exists()){
+    apply plugin: 'com.google.gms.google-services'
+}

scripts/build-android-debug.sh

@@ -1,5 +1,4 @@
 #!/usr/bin/env bash
 flutter channel stable
 flutter upgrade
-truncate -s $(head -n -2 android/app/build.gradle | wc -c) android/app/build.gradle
-flutter build apk --debug -v
+flutter build apk --debug -v