Remove shebang lines from bin/ scripts for performance

[cmcginty]

All scripts in bin/ are called through pyenv therefore the shebang
lines are not necessary. On some systems this provides a measurable
increase in performance of the shell prompt.

Fixes #259

On my system this removes 400ms of run time from the pyenv sh-activate
command.

[blueyed]

As per pyenv/pyenv#1153 (comment) I still think this is not really necessary.

@cmcginty can you provide timing information via python -m timeit "__import__('subprocess').Popen(['pyenv', 'sh-activate']).communicate()" (and other commands) with and without this change?

If this is a workaround for carbonblack etc, it might still make sense to merge it.
But in general pyenv/pyenv#357 would be better then.
It would also be good to get this into rbenv/pyenv first, to not spread the discussion everywhere.

[doron-cohen]

Hi, This is not only for carbon black users. I removed pyenv init from my profile because it is very slow and takes ~600ms to load the prompt which is an very annoying.
this fix helps in my case too and I have no antivirus on my machine

[native-api]

This would break Fish as per pyenv/pyenv#1337