Revert "Add subplugins.json"

This reverts commit f8e30239.

db/subplugins.json

-{
-  "plugintypes": {
-    "lifecycletrigger": "admin\/tool\/lifecycle\/trigger",
-    "lifecyclestep": "admin\/tool\/lifecycle\/step"
-  }
-}

db/subplugins.php

@@ -23,4 +23,7 @@
  */
 defined('MOODLE_INTERNAL') || die();
 
-$subplugins = json_decode(readfile(__DIR__ . '/subplugins.json'));
+$subplugins = array(
+    'lifecycletrigger' => 'admin/tool/lifecycle/trigger',
+    'lifecyclestep' => 'admin/tool/lifecycle/step',
+);