Remove ember-tether (#1438)

Author: elwayman02

package.json

@@ -67,7 +67,6 @@
     "ember-router-scroll": "^4.1.2",
     "ember-set-helper": "^2.0.1",
     "ember-svg-jar": "^2.4.2",
-    "ember-tether": "^2.0.1",
     "ember-truth-helpers": "^3.0.0",
     "esm": "^3.2.25",
     "execa": "5.1.1",