How do I remove the mark in and mark out?

I'll give you actually useful advice. Try right clicking the marker and clearing the "in" and "out". Maybe you have to clear each once, maybe you have to clear one of them twice, i'm not sure. But this seems to be the solution. I'm not sure why I could find an answer for like... 4 years, but I hope this helps some one out. 

Try this: Close Premiere e start it again. 

All of the marker commands are on the Markers menu, so when you’re in a sequence and it has In point and Out point markers set, the Clear marker commands are available on that menu. As usual, their keyboard shortcuts are listed to the right of the commands.

You can also see the logic behind the Clear shortcuts; they’re the same as the Mark shortcuts but adding the Option (Mac) or Alt (Windows) key. So if you already memorized the Mark shortcuts, to clear markers just add Option/Alt to the same shortcuts.

A lot of times you can right click on a mark or item and you get a drop down menu that gives options , like 'delete' or 'remove' etc.