fix: delete old files & folders on each js_run_devserver sync

[gregmagolan]

js_run_devserver is aware of all of the files to sync per sync so it is easy enough to delete files that are no longer synced out of the custom sandbox on each sync.

Test plan

• Covered by existing test cases
• Manual testing; please provide instructions so we can reproduce:

Run ibazel run //:dev in e2e/webpack_devserver and manually delete a synced file such as src/404.html. Expected output is:

Deleting src/404.html
1 file/folder deleted in 1 ms
+ Syncing 18 files && folders...
+ Syncing 6 non-node_modules files & folders...
Skipping file mylib/index.js since its timestamp has not changed
Skipping file mylib/package.json since its timestamp has not changed
Skipping file package.json since its timestamp has not changed
Skipping file src/index.html since its timestamp has not changed
Skipping file src/index.js since its timestamp has not changed
Skipping file webpack.config.js since its timestamp has not changed
+ Syncing 2 first party package store dep(s)
Skipping file node_modules/.aspect_rules_js/@mycorp+mylib@0.0.0/node_modules/@mycorp/mylib since its timestamp has not changed
Skipping file node_modules/.aspect_rules_js/@mycorp+mypkg@0.0.0/node_modules/@mycorp/mypkg/index.js since its timestamp has not changed
Skipping file node_modules/.aspect_rules_js/@mycorp+mypkg@0.0.0/node_modules/@mycorp/mypkg/package.json since its timestamp has not changed
+ Syncing 10 other node_modules files
Skipping file mylib/node_modules/chalk since its timestamp has not changed
Skipping file node_modules/@bazel/ibazel since its timestamp has not changed
Skipping file node_modules/html-webpack-plugin since its timestamp has not changed
Skipping file node_modules/lodash since its timestamp has not changed
Skipping file node_modules/webpack-cli since its timestamp has not changed
Skipping file node_modules/webpack-dev-server since its timestamp has not changed
Skipping file node_modules/webpack since its timestamp has not changed
Skipping file node_modules/@mycorp/mylib since its timestamp has not changed
Skipping file node_modules/.aspect_rules_js/@mycorp+mypkg@0.0.0/node_modules/chalk since its timestamp has not changed
Skipping file node_modules/@mycorp/mypkg since its timestamp has not changed