Remove an expensive database call only used for tracing prupose

[BillCarsonFr]

mark_request_as_sent of the BackupMachine was doing a call to store_inbound_group_session_count just for tracing purpose.
On a test setup with 100k room keys, this call to count is taking 1955ms, in comparison mark_inbound_group_sessions_as_backed_up is taking 300ms.
It's making mark as sent for backup take long for nothing

• Public API changes documented in changelogs (optional)

Signed-off-by:

[bnjbvr]

For performance improvements, please provide a benchmark in a separate commit, a run before the patch, and a run after the patch. Thanks in advance!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (45bdbf5) 83.41% compared to head (541d918) 83.41%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2977      +/-   ##
==========================================
- Coverage   83.41%   83.41%   -0.01%     
==========================================
  Files         222      222              
  Lines       23150    23149       -1     
==========================================
- Hits        19311    19310       -1     
  Misses       3839     3839              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[BillCarsonFr]

For performance improvements, please provide a benchmark in a separate commit, a run before the patch, and a run after the patch. Thanks in advance!

AFAIK there are no benchmark for indexeddb

[richvdh]

lgtm