Stop viewport-size logging to appEvents (data collection complete)

Elazar fleet directive 2026-07-07: enough viewport telemetry collected across mars/pluto/venus. REMOVE the client viewport-size logging that writes to appEvents (the banded viewport telemetry path). Small REVERSIBLE removal (Class-S: single concern, one-owner, security-inert). Keep the removal clean — drop the client emit + any now-dead server handler; leave historical rows in place (retention prunes them). Cross-ref mem pluto-client-env-telemetry-privacy. Prereq/pairs with PLUTO-537 (which consumes the collected distribution before we stop adding to it — pull the distribution FIRST, then this removal can land).