Remove unneeded ember-symbol-observable and symbol-observable

[juwara0]

This project uses semver, please check the scope of this pr:

• [ ] #none# - documentation fixes and/or test additions
• [X] #patch# - backwards-compatible bug fix
• [ ] #minor# - adding functionality in a backwards-compatible manner
• [ ] #major# - incompatible API change

CHANGELOG

• Removed unneeded ember-symbol-observable and symbol-observable that were brought in via ember-frost-bunsen via the blueprints of ember-redux-shim

[notmessenger]

👍