[wrappers] shellenv should not create bin wrappers

[mikeland73]

Summary

Fixes #1073

The underlying cause of #1073 is that we were creating bin wrappers in shellenv which can get called a lot (and in parallel) this was leading to race conditions.

We should still try to limit shellenv calls (because they slow things down), but this fixes the race condition.

cc: @bketelsen

How was it tested?

Since I could not repro race condition, I created a setup that simulated it:

• Wrote some testing code that would save a file to /tmp every time create wrappers is called.
• Setup the environment to call a bin wrapper for every command
• Before change, saw new /tmp file being created on every command.
• After change, no new /tmp file was getting created.
• Tested devbox install for sanity.