Remove additional cruft from Tailwind config

These literally weren't hurting anything but the upgrade guide
suggests toasting them, so might as well do it while I'm in here.

web/tailwind.config.js

@@ -1,7 +1,6 @@
 const defaultTheme = require('tailwindcss/defaultTheme')
 
 module.exports = {
-  mode: 'jit',
   content: [
     './pages/**/*.{js,ts,jsx,tsx}',
     './components/**/*.{js,ts,jsx,tsx}',
@@ -20,9 +19,6 @@ module.exports = {
       },
     },
   },
-  variants: {
-    extend: {},
-  },
   plugins: [
     require('@tailwindcss/forms'),
     require('@tailwindcss/typography'),