(remove) unused library

package.json

@@ -52,7 +52,6 @@
     "material-ui-search-bar": "^1.0.0-beta.13",
     "notistack": "https://github.com/gnosis/notistack.git#v0.9.4",
     "optimize-css-assets-webpack-plugin": "5.0.3",
-    "polish": "^0.2.3",
     "qrcode.react": "1.0.0",
     "react": "16.12.0",
     "react-dom": "16.12.0",

src/theme/mui.js

@@ -1,6 +1,5 @@
 // @flow
 import { createMuiTheme } from '@material-ui/core/styles'
-import { rgba } from 'polished'
 import {
   boldFont,
   bolderFont,