Undoes the work introduced in #5616. 

This plugin adds around 40-50 seconds to webpack build times and has caused confusion (see #13834).

Also adds an eslint rule to prevent importing `lodash` bundle: getsentry/eslint-config-sentry#46

| -- | With Plugin | Without Plugin | Difference | lodash-es | lodash-es + react-mentions |
| -- | ----------- | -------------- | ---------- | --------- | - |
| app.js | 739051 | 739120 | 0% | | |
| app.js.gzip | 184017 | 184040 | 0% | | 186949 |
| vendor.js | 2076311 | 2090876 | +0.7% | 2089352 |
| vendor.js.gizp | 375718 | 380446 | + 1.2% | 380630 | 380476 |
| build time (w/ stats) | 316s | 466s | + 47% | |
| build time (env=prod) | 335s | 198s | n/a | |

Currently, there is no sizable difference between `lodash-es` and `lodash` -- we should revisit this in the future.