You could remove them, but it would be considered a customization. Some of the indexes have comments associated with them that should give you some idea what they're for. Depending on the functionality your users currently use, you can always expect that you will have unused indexes on many tables. Disk is cheap, though, so customizing to save space probably isn't worth it.
You can view the comments in app designer, or use SQL--something like
select indexid, idxcomments from psindexdefn where recname='VCHR_ACCTG_LINE' order by indexid;
If you do want to remove an index, you should set the Platform flag to none (Not Active) in app designer (Tools->Data Administration->Indexes then highlight the index you want to remove and click on Edit Index). If you then use Build->Current Definition and select Create Indexes (make sure the Build Settings say Create Indexes only if modified), I think it will generate the DROP INDEX statements for you.
If you just drop the index in Oracle you will get DDDAUDIT errors. If you completely remove the index definition in app designer, it probably won't be identified as a customization in an upgrade and the indexes will reappear if you aren't careful.