This treats lines differing only in case as the same, keeping one and discarding the rest.
What it catches that exact matching misses
Running Shoes, running shoes and RUNNING SHOES are three distinct lines to an exact comparison and one entry here.
Why case inconsistency is so common
Different sources format differently. Search queries arrive as typed, keyword tools title-case their exports, and manually entered data reflects whoever typed it.
Which version survives
Usually the first occurrence. If a particular casing matters for display, normalise the whole list to that form rather than relying on which copy happened to come first.
Try it: Remove Duplicates (Case-Insensitive) on SeoWolf's Notepad.