kbfsedits: clarify rename revision variable name
kbfsedits: clarify rename revision variable name

Suggested by songgao.

Issue: #19869

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client