Remove fs and os usage from Mobile Builds plugin

Summary: Changelog: Expose env info and FS rm command to flipper plugins.

Reviewed By: mweststrate

Differential Revision: D32988478

fbshipit-source-id: 3d0233f9eb34d3478b07e39b9401c0e30ca95135

docs/extending/flipper-plugin.mdx

@@ -1160,6 +1160,12 @@ path.normalize('/foo/bar//baz/asdf/quux/..');
 // Returns: '/foo/bar/baz/asdf'
 ```
 
+### uuid
+
+Usage: `uuid()`
+
+Returns UUID V4.
+
 ## TestUtils
 
 The object `TestUtils` as exposed from `flipper-plugin` exposes utilities to write unit tests for Sandy plugins.