Remove Flow support

We no longer use Flow, so this removes linting and compiling support. New code
should use TypeScript for static typing.

package.json

@@ -110,10 +110,8 @@
     "@babel/plugin-proposal-export-default-from": "^7.12.1",
     "@babel/plugin-proposal-numeric-separator": "^7.12.7",
     "@babel/plugin-proposal-object-rest-spread": "^7.12.1",
-    "@babel/plugin-transform-flow-comments": "^7.12.1",
     "@babel/plugin-transform-runtime": "^7.12.10",
     "@babel/preset-env": "^7.12.11",
-    "@babel/preset-flow": "^7.12.1",
     "@babel/preset-react": "^7.12.10",
     "@babel/preset-typescript": "^7.12.7",
     "@babel/register": "^7.12.10",
@@ -150,7 +148,6 @@
     "eslint": "7.18.0",
     "eslint-config-matrix-org": "^0.2.0",
     "eslint-plugin-babel": "^5.3.1",
-    "eslint-plugin-flowtype": "^5.2.0",
     "eslint-plugin-react": "^7.22.0",
     "eslint-plugin-react-hooks": "^4.2.0",
     "glob": "^7.1.6",