What is this thing and how to remove it?

[John28850210ubid]

[Warren Heaton]

The horizontal bar at the top of the Playhead represents the length (or width) of a single frame (the smallest unit of time) along the Time Ruler while the thin vertical line represents the start of the frame.  

It's a visual part fo the user interface that cannot be removed.

[Ann Bens]

Set to Show AudioTime Units its even smaller: 1/48000 of a second.