-Choose the automask tool (The wizard's wand), no soft edge, no fill holes, only contiguous
-Click into the first letter you want to remove, hold down shift, click into the other letters.
-Tool > Mask > Expand mask by 2 pixels or so.
-filter > other > median, radius 6 looked fine for me. Not all white areas were deleted, but most, and the filled-in parts did match quite good to the background.
-The clone brush will do the rest: Choose a good source area an clone a while with still activated mask
-..then delete the mask (ctrl+D) and clone a bit more without it where needed