remove unused react-observer-polyfill, and fix some typescript unused imports

Author: williamstein

src/packages/frontend/frame-editors/code-editor/codemirror-editor.tsx

@@ -14,7 +14,6 @@ codemirror editor instance mainly for use in a frame tree.
 
 import { SAVE_DEBOUNCE_MS } from "./const";
 import { Map, Set } from "immutable";
-import { is_safari } from "../generic/browser";
 import * as CodeMirror from "codemirror";
 import {
   React,

src/packages/frontend/frame-editors/frame-tree/frame-tree.tsx

@@ -32,9 +32,7 @@ import { copy, hidden_meta_file, is_different } from "@cocalc/util/misc";
 import { delay } from "awaiting";
 import { Map, Set } from "immutable";
 import React from "react";
-
 import {
-  ReactDOM,
   redux,
   Rendered,
   useState,
@@ -44,7 +42,6 @@ import { Loading } from "@cocalc/frontend/components";
 import { AvailableFeatures } from "@cocalc/frontend/project_configuration";
 import { Actions } from "../code-editor/actions";
 import { cm as cm_spec } from "../code-editor/editor";
-import { is_safari } from "../generic/browser";
 import { TimeTravelActions } from "../time-travel-editor/actions";
 import { FrameContext } from "./frame-context";
 import { FrameTreeDragBar } from "./frame-tree-drag-bar";

src/packages/frontend/frame-editors/html-editor/iframe-html.tsx

@@ -17,7 +17,6 @@ Component that shows rendered HTML in an iFrame, so safe and no mangling needed.
 import $ from "jquery";
 import { Set } from "immutable";
 import { delay } from "awaiting";
-import { is_safari } from "../generic/browser";
 import {
   change_filename_extension,
   is_different,

src/packages/frontend/package.json

@@ -151,7 +151,6 @@
     "react-redux": "^8.0.5",
     "react-timeago": "^7.2.0",
     "react-virtuoso": "^4.9.0",
-    "resize-observer-polyfill": "^1.5.1",
     "sha1": "^1.1.1",
     "shallowequal": "^1.1.0",
     "shell-escape": "^0.2.0",