Use 389-ds provided method for file limits tuning

Previously IPA would set the LimitNOFILE value to 8192 to increase
the number of concurrent clients. 389-ds-base does this by default
as of 1.3.7.0.

Remove the IPA-specific tuning and rely on the out-of-the-box
389-ds-base tuning.

Bump the required version of 389-ds-base to 1.3.7.0.

Any other tuning added by 389-ds-base will result in a
dirsrv.systemd.rpmsave file which admins will need to merge
in manually, like typical .rpmsave config changes.

https://pagure.io/freeipa/issue/6994

Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipaplatform/debian/services.py

@@ -121,10 +121,6 @@ class DebianSysvService(base_services.PlatformService):
     def remove():
         return True
 
-    @staticmethod
-    def tune_nofile_platform():
-        return True
-
 
 # For services which have no Debian counterpart
 class DebianNoService(base_services.PlatformService):