Replace ember-cli-eslint with direct eslint usage.

`yarn lint:js` is used by CI to enforce linting, removing
ember-cli-eslint effectively means that no linting tests will be done as
part of the build.

This works around a long standing issue in ember-cli-eslint where the
directory provided to eslint when linting is incorrect, which throws an
error when `eslint-config-prettier` attempts to read the `.editorconfig`
file to infer base settings.

package.json

@@ -66,7 +66,6 @@
     "ember-cli-app-version": "^3.2.0",
     "ember-cli-blueprint-test-helpers": "^0.18.3",
     "ember-cli-dependency-checker": "^3.0.0",
-    "ember-cli-eslint": "^4.2.3",
     "ember-cli-htmlbars": "^3.0.0",
     "ember-cli-htmlbars-inline-precompile": "^1.0.3",
     "ember-cli-inject-live-reload": "^1.8.2",
@@ -91,6 +90,7 @@
     "ember-source": "~3.0.0",
     "ember-source-channel-url": "^1.1.0",
     "ember-try": "^1.0.0-beta.3",
+    "eslint": "^5.3.0",
     "eslint-config-prettier": "^2.9.0",
     "eslint-plugin-node": "^7.0.1",
     "eslint-plugin-prettier": "2.6.2",