refactor: remove support for DOKKU_SCALE file

It has been replaced by the 'formations' key within the 'app.json' file format.

tests/apps/config/DOKKU_SCALE

@@ -1,2 +0,0 @@
-# test comment
-web=1

tests/apps/config/app.json

@@ -0,0 +1,7 @@
+{
+    "formation": {
+        "web": {
+            "quantity": 1
+        }
+    }
+}

tests/apps/dockerfile-app-json-formations/app.json

@@ -0,0 +1,7 @@
+{
+    "formation": {
+        "web": {
+            "quantity": 1
+        }
+    }
+}

tests/apps/dockerfile-dokku-scale/DOKKU_SCALE

@@ -1 +0,0 @@
-web=1

tests/apps/nodejs-worker/DOKKU_SCALE

@@ -1,2 +0,0 @@
-web=0
-worker=1

tests/apps/nodejs-worker/app.json

@@ -0,0 +1,10 @@
+{
+    "formation": {
+        "web": {
+            "quantity": 0
+        },
+        "worker": {
+            "quantity": 1
+        }
+    }
+}

tests/unit/ps-dockerfile-2.bats

@@ -12,13 +12,13 @@ teardown() {
   global_teardown
 }
 
-@test "(ps:scale) dockerfile dokku-scale" {
+@test "(ps:scale) dockerfile app-json formations" {
   run /bin/bash -c "dokku ps:scale $TEST_APP web=2"
   echo "output: $output"
   echo "status: $status"
   assert_success
 
-  deploy_app dockerfile-dokku-scale
+  deploy_app dockerfile-app-json-formations
   CIDS=""
   for CID_FILE in $DOKKU_ROOT/$TEST_APP/CONTAINER.web.*; do
     CIDS+=$(<$CID_FILE)