thanos: don't manage limitnofile for thanos-store

Stop managing limitnofile, Bookworm systemd default is soft 1024 and
hard 524288.  Further, golang >= 1.19 'os' package bumps soft to hard
limit automatically (cfr golang/go#46279)

For example thanos-query-frontend where we don't explicitly set
limitnofile:

  root@titan2001:~# cat /proc/$(pgrep -f "thanos query-frontend")/limits | grep files
  Max open files            524288               524288               files
  root@titan2001:~# systemctl show thanos-query-frontend | grep -i limitnofile
  LimitNOFILE=524288
  LimitNOFILESoft=1024

Bug: T346950
Change-Id: I3df68d63c66293e4425cb7e67670e44459c4d474

modules/thanos/templates/initscripts/thanos-store.systemd.erb

@@ -3,4 +3,3 @@
 ExecStart=
 # Use = for min/max time options since their values can start with -
 ExecStart=/usr/bin/thanos store --http-address <%= @http_address %> --grpc-address <%= @grpc_address %> --data-dir <%= @data_dir %> --index-cache.config-file <%= @cache_config_file %> --objstore.config-file <%= @objstore_config_file %> <%= @min_time ? "--min-time=#{@min_time}" : '' %> <%= @max_time ? "--max-time=#{@max_time}" : '' %> <%= @consistency_delay ? "--consistency-delay=#{@consistency_delay}" : '' %>
-LimitNOFILE=10240