Override posthog type definitions to point to a locally fixed type definition file

Posthog's type definitions refer to types in transitive dependencies we don't want to include.

Clone posthog.d.ts locally, remove the offending types from it, and provide an overriding mapping in tsconfig.

If this proves annoying to maintain, posthog.d.ts could just be an empty file.

package.json

@@ -125,7 +125,6 @@
     "@matrix-org/olm": "https://gitlab.matrix.org/api/v4/projects/27/packages/npm/@matrix-org/olm/-/@matrix-org/olm-3.2.3.tgz",
     "@peculiar/webcrypto": "^1.1.4",
     "@sinonjs/fake-timers": "^7.0.2",
-    "@sentry/types": "^6.2.2",
     "@types/classnames": "^2.2.11",
     "@types/commonmark": "^0.27.4",
     "@types/counterpart": "^0.18.1",
@@ -168,7 +167,6 @@
     "matrix-web-i18n": "github:matrix-org/matrix-web-i18n",
     "react-test-renderer": "^17.0.2",
     "rimraf": "^3.0.2",
-    "rrweb": "^0.9.9",
     "stylelint": "^13.9.0",
     "stylelint-config-standard": "^20.0.0",
     "stylelint-scss": "^3.18.0",