Deprecate 32-bit Arm support

[alexellis]

Why do you need this?

With containerd 1.7.18, I was unable to build new binaries on a 32-bit OS.

containerd is not built for 32-bit Arm, so I have to make builds available by running lengthy manual tasks on a Raspberry Pi with a 32-bit OS available. I no longer wish to do this, and the 64-bit OS should be a default now.

Let me know if you feel like this affects you in some way.

Migration instructions - copy files in /var/run/faasd and /var/run/faasd-provider as a backup. Then reflash with new OS and do a fresh install. Redeploy functions and secrets after that.

[alexellis]

This change has been made in release 0.19.0 onwards.