You have logretain set to recovery but have not turned the userexit on. IBM provides sample userexits under $insthome/sqllib/samples/c and this functionality may be activated as follows.
db2uext2.cadsm <<-->> Archive to TSM
db2uext2.cdisk <<-->> Archive to disk
db2uext2.ctape <<-->> Unix Tape archive
db2uext2.cxbsa <<-->> Archive to Legato Networker(AIX)
Depending on the method of archiving, copy the required file to db2uext2.c
Edit db2uext2.c to customize
and create these directories.
Compile and link db2uext2.c to db2uext2.exe and copy this file to $insthome/sqllib/bin/
Activate it by updating the db cfg parameter USEREXIT to ON
This will archive the logs to another directory and you could create a job to clean up this directory based on the retention period of the online backups.
A word of caution about deleting log files when you are doing online backups - if you do not have the log files related to the online backup(ie when the backup was running) you may not be able to recover from this backup. After recovering,. the database will remain in rollforward pending. A good practice is to truncate the logs before the backup and truncate again right after the backup(if you have the registry variable DB2_DISABLE_FLUSH_LOG set ot ON). If the registry variable is not set or set to off, then db2 will truncate the logs after completing the backups. These logs are required to recover from the online backup. This needs to be addressed if you are considering deleting old logs.