remove AIX support - see #10

`npm ci` and `npm install --force` have a bug where it attempts to install
the AIX-specific dependency even on non-AIX platforms, which results in a
huge block of gyp errors on all other platforms.

This commit removes AIX and the native dependency again, eliminating
these type of errors.

Author: silverwind

aix.js

@@ -10,7 +10,6 @@ if ([
   "openbsd",
   "sunos",
   "win32",
-  "aix"
 ].indexOf(platform) !== -1) {
   const families = require(`./${platform}`);
   module.exports.v4 = () => families.v4();

index.js

@@ -15,9 +15,6 @@
     "execa": "^1.0.0",
     "ip-regex": "^2.1.0"
   },
-  "optionalDependencies": {
-    "idb-connector": "^1.1.8"
-  },
   "devDependencies": {
     "eslint": "^5.5.0",
     "eslint-config-silverwind": "^2.0.9",
@@ -31,8 +28,7 @@
     "linux",
     "openbsd",
     "sunos",
-    "win32",
-    "aix"
+    "win32"
   ],
   "files": [
     "index.js",
@@ -42,8 +38,7 @@
     "linux.js",
     "openbsd.js",
     "sunos.js",
-    "win32.js",
-    "aix.js"
+    "win32.js"
   ],
   "keywords": [
     "default gateway",