chore: remove unused IN-1195 aggregate pipes for now

Contributors/Popularity/Development collection tabs are hidden in the
insights UI while IN-1195 is being reworked - removing the corresponding
Tinybird pipes so the PR doesn't ship dead backend code. The
showAggregateTabs migration and collection_insights_aggregate.pipe
(IN-1193's header metrics, already deployed and working) stay.

Signed-off-by: Gašper Grom <gasper.grom@gmail.com>

Author: gaspergrom