Revert inclusion of pre-bundled node-pre-gyp into Git repo.

This reverts commit e0d8acc.

Author: Moritz Raguschat

package.json

@@ -9,7 +9,7 @@
   },
   "scripts": {
     "test": "mocha",
-    "install": "./node_modules/node-pre-gyp/bin/node-pre-gyp install --fallback-to-build"
+    "install": "node-pre-gyp install --fallback-to-build"
   },
   "bin": {
     "node-pre-gyp": "./node_modules/node-pre-gyp/bin/node-pre-gyp"