Under the assumption that you do not want it to appear anywhere, the simplest thing to do is to edit the default master page (not first) in engrave mode. Double click on the master page icon itself on the right, select the header text and delete it; apply and save.
The flow title you label in your picture (below the project title, and with the "1. " at the start) is known as a flow heading. By default, they are set to appear automatically above the start of each flow - they’re really useful in projects with multiple flows, particularly in parts where the 2nd flow might start halfway down a page after the 1st flow.
You can hide/show them by default in each layout independently, and if you like, you can set your default layout options not to show them at all (if you mostly deal with single-flow projects, this might be preferable). You can also select the frame that contains the flow heading in Engrave mode and delete, but be aware this creates a page override and any further changes you make to the master page do not get reflected on pages with overrides.
For the flow title at the tops of other pages (i.e. p2 onwards) that requires editing the Default master page as described above.