Where are those borders? The only thing there except some data is Freeze Panes at cell E23 activated. This results topmost 22 rows and leftmost 4 columns not scrolled and always visible for user. The lines between movable and non-movable parts of sheet are marked as lines. NB! Those aren't borders!

You can switch this feature On/Of from Freeze Panes button in Wiew menu. The currently active cell when you activate this feature will determine how many columns and/or rows will be freezed. It is usually used to make table headers always visible, and/or make some leftmost columns (which may work as row identifiers) to be always visible in case the table is too wide otherwise.