Convert name to lower case for removePermission; Fixes BUKKIT-3726

Permissions are stored as lower case names and referenced as such in all
appropriate methods but removePermission. This changes removePermission
to also convert names to lower case to be consistent with the rest of
the API.

By: Max A <maximilian.ammann@googlemail.com>

paper-api/src/main/java/org/bukkit/plugin/SimplePluginManager.java

@@ -581,11 +581,11 @@ public final class SimplePluginManager implements PluginManager {
     }
 
     public void removePermission(Permission perm) {
-        removePermission(perm.getName().toLowerCase());
+        removePermission(perm.getName());
     }
 
     public void removePermission(String name) {
-        permissions.remove(name);
+        permissions.remove(name.toLowerCase());
     }
 
     public void recalculatePermissionDefaults(Permission perm) {