Temporarily remove exec-all plugin (#121)

NOTE: Krew isn't handling removal of an installed plugin from the plugin
index right now.

We're removing this to bypass the CLA requirement of the original contributor
since the repo is being transferred to CNCF. kubernetes/org#599

I will add package plugin myself after the migration is complete.

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>