The ARCH.ARCLOG is used as a history file. It can be moved as required and the data is not managed so you can delete the file and allocate a new one.
//STEP1 EXEC PGM=$FORMAT
//SYSPRINT DD SYSOUT=*
//$LOG DD DSN=your.prefix.ARCLOG,
The file itself is used for date controlled backup and archive functions which most CA ASM2 customers never use anymore.