Remove legacy codebase (#4844)

* Remove legacy codebase

* Remove legacy docs

* Fixed memory leak in timer spec

* Remove Angular dependency

* Removed adapter layer

* Removed legacy support plugin from main Open MCT repo

* Restored TelemetryAPI.js which had been inexplicably deleted?

* Fix linting error

* Drop line coverage threshold due to removed code

* Added a section on Open MCT 2.0.0 to the readme

.eslintrc.js

@@ -1,4 +1,4 @@
-const LEGACY_FILES = ["platform/**", "example/**"];
+const LEGACY_FILES = ["example/**"];
 module.exports = {
     "env": {
         "browser": true,