Not quite sure what you mean.
If you mean the grey bar covering the entire timeline that is the Work Area Bar.
Doubel click on it then it will become the size of the timeline that is viewed.
Now you are able to see the yellow ends which you can drag with the mouse.
For more on the work area bar.
If you mean the little yellow bar right of the playhead. That respresents one frame. You cannot get rid of that.
You could be referring to the actual appearance of the playhead when zoomed way in. At a normal zoom size, you would not normally see the small bar jutting ahead ahead the playhead. The playhead appears this way because it is displaying exactly one frame at any one time. At that zoom level, you can see that it represents a single frame quite accurately.