chore: remove ARM support

Building/testing for ARM does not happen often - the only runtime environment is Raspberry PI, which supports ARM64 - and complicates support for a ton of features. Aside from that, CI runs are much longer for ARM Dokku images, often reaching 15-20 minutes or just timing out completely.

Rather than support an architecture that doesn't have much usage by maintainers and has a lot of maintenance burden, we're removing the platform.

plugins/git/functions

@@ -57,10 +57,6 @@ git_trigger_build() {
         dokku_log_warn "Herokuish builder not supported on $ARCHITECTURE servers."
         dokku_log_warn "Switching to pack builder."
         BUILDER="pack"
-      elif [[ "$ARCHITECTURE" == "armhf" ]]; then
-        dokku_log_warn "Herokuish builder not supported on $ARCHITECTURE servers."
-        dokku_log_warn "Consider using a Dockerfile to build your app."
-        return 1
       fi
     fi
   fi