package: remove ember/render-modifiers devDep

Right now, we depend on the @ember/render-modifiers package, but do not
actually use it.  For reference, it looks like the original dep/usage
was added in `Commit: c0f373b` and then that usage was subsequently
removed in `Commit: 459a576`.

As such, we should just be able to remove the dependency.

Author: Geodewd549

package-lock.json

@@ -25,7 +25,6 @@
   },
   "devDependencies": {
     "@ember/optional-features": "^2.0.0",
-    "@ember/render-modifiers": "^1.0.2",
     "@ember/test-helpers": "^2.6.0",
     "@glimmer/component": "^1.0.4",
     "@glimmer/tracking": "^1.1.1",