It's pretty simple in Photoshop. I'll show how it's done quickly in steps in case anybody else is wondering (bear in mind I'm not Photoshop expert so there's probably a more professional way than this).
1. Cut out the text using the Polygonal Lasso Tool, cut it and paste it into its own image.
2. Use the magic wand tool to select a blue part of the background using quite a high tolerance because we want to get all of the background which isn't text, I used 100.
3. Now we want to select the text so we inverse the selection and then modify the edge to expand it by a couple of pixels:
4. If you didn't expand it you'd end up with a lot more artefacts of the text. This leaves us with this:
5. Now we want to use the content-aware fill option in Photoshop (Edit > Fill > Content-Aware, or Shift+F5) which is actually very useful in the right circumstances and it's something which quite a lot of people don't seem to know exists:
6. After one pass we end up with this (as you can it's removed quite a lot of the text already):
7. Keep doing that same fill a few more times and we end up with this (pretty much all gone now):
8. Now we just need to clean it up a bit to get rid of what's left of the text. To do that I used the smudge tool because we didn't really need to be massively intricate. The important thing here is to smudge it only horizontally because sky has strata which you don't want to blend into one another.
9: Now we have it almost done, we just need to put it back into the original image:
10. Just copy the whole thing and paste it back into your original image, switch the layers so your new, clean sky one is behind the original and you're just left with a little bit of cleaning up and then you're done.
So maybe a couple of minutes to remove all that text quite effectively I think.