mw-install-sqlite: .sqlite deletion had a race condition

When running multiple jobs in parralel, they all ends up using a sqlite
file in something like /tmpfs/<jobname>. Deleting all sqlite files there
would thus cause a race condition between jobs where a new job might
delete the sqlite file of a currently running job.

Instead of rm, use find to delete sqlite files that are older than an
hour.

Change-Id: I95ef783cc42beb19c86de2b524f7e04a962c0105