Remove extra-lint

- standard enforces 'let' and 'const' now
- I've never been a fan of the <100 chars per line rule since it violates the standard philosophy. it should be possible to write conformant code without needing a tool, so 'magic numbers' like 'no more than X lines/chars/statements' are not ideal

package-lock.json

@@ -3969,12 +3969,6 @@
         "ansi-colors": "^4.1.1"
       }
     },
-    "ensure-posix-path": {
-      "version": "1.1.1",
-      "resolved": "https://registry.npmjs.org/ensure-posix-path/-/ensure-posix-path-1.1.1.tgz",
-      "integrity": "sha512-VWU0/zXzVbeJNXvME/5EmLuEj2TauvoaTz6aFYK1Z92JCBlDlZ3Gu0tuGR42kpW1754ywTs+QB0g5TP0oj9Zaw==",
-      "dev": true
-    },
     "err-code": {
       "version": "2.0.3",
       "resolved": "https://registry.npmjs.org/err-code/-/err-code-2.0.3.tgz",
@@ -7325,16 +7319,6 @@
         }
       }
     },
-    "matcher-collection": {
-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/matcher-collection/-/matcher-collection-2.0.1.tgz",
-      "integrity": "sha512-daE62nS2ZQsDg9raM0IlZzLmI2u+7ZapXBwdoeBUKAYERPDDIc0qNqA8E0Rp2D+gspKR7BgIFP52GeujaGXWeQ==",
-      "dev": true,
-      "requires": {
-        "@types/minimatch": "^3.0.3",
-        "minimatch": "^3.0.2"
-      }
-    },
     "material-ui": {
       "version": "0.20.2",
       "resolved": "https://registry.npmjs.org/material-ui/-/material-ui-0.20.2.tgz",
@@ -11415,18 +11399,6 @@
         "he": "^1.1.0"
       }
     },
-    "walk-sync": {
-      "version": "2.2.0",
-      "resolved": "https://registry.npmjs.org/walk-sync/-/walk-sync-2.2.0.tgz",
-      "integrity": "sha512-IC8sL7aB4/ZgFcGI2T1LczZeFWZ06b3zoHH7jBPyHxOtIIz1jppWHjjEXkOFvFojBVAK9pV7g47xOZ4LW3QLfg==",
-      "dev": true,
-      "requires": {
-        "@types/minimatch": "^3.0.3",
-        "ensure-posix-path": "^1.1.0",
-        "matcher-collection": "^2.0.0",
-        "minimatch": "^3.0.4"
-      }
-    },
     "warning": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/warning/-/warning-3.0.0.tgz",