you can only see it in viewport mode. I cant find it in outliner or anywhere else to delete it. So how do i get rid of it?
You do not delete them, i think you are using default (from engine) level.
Instead make new level, save it in YOUR content folder. Then modify.
Or even better create new level that is basic ie. empty with skybox only. Then add landscape.
But if you are starting some code project (like game) code first do not bother with detailed level until you have some gameplay and know speed of character, jumps etc.
Ps.
Try rebuilding level, that may be some leftover cell from before you deleted stuff. However starting from that default landscape level (one in engine) is bad idea.