Merge bitcoin#21695: Remove no longer used contrib/bitcoin-qt.pro from the repo

5f2be6e Remove no longer used contrib/bitcoin-qt.pro from the repo (Hennadii Stepanov)

Pull request description:

  From [IRC](http://www.erisian.com.au/bitcoin-core-dev/log-2021-04-15.html#l-209):
  > \<hebasto> wumpus: I cannot see any way how the `contrib/bitcoin-qt.pro` is used in the  translation process, neither in the main repo nor in https://github.com/bitcoin-core/bitcoin-maintainer-tools. Besides it looks outdated and unmaintained. May I ask you to confirm/deny my assumption?
  > \<wumpus> hebasto: it is not used for anything, it exists to be able to edit the qt forms in qt designer nothing more
  > \<wumpus> i'm not sure if it is even *necessary* for that, but it is why it is there
  > \<hebasto> wumpus: thanks, qt designer does not need *.pro file at all
  > \<hebasto> maybe qt creator does
  > \<wumpus> feel free to create a PR to remove it, best way to find out if someone wants to keep it, you are right it hasn't been updated in a long time
  > \<hebasto> ok
  > \<wumpus> fwiw, the only question i get about it ever is why it exists
  > \<hebasto> it was in use with `qmake` years ago (what I found digging into the repo history)
  > \<wumpus> yes, that was the original reason, but when we switched to automake it was kept around for use w/ qt's GUI tools
  > \<hebasto> I've noticed it in https://github.com/bitcoin/bitcoin/blame/master/doc/translation_process.md#L25
  > \<wumpus> what it says there is definitely not true anymore

ACKs for top commit:
  laanwj:
    ACK 5f2be6e
  jarolrod:
    ACK 5f2be6e

Tree-SHA512: 7c105612f28185097fee9e4108b162b4c8b07cc527f4438bdf5bcab08c65421ea301de8584d58770cd113fa871f6781daa8145bd6463278523449e28bfc49d06

Author: fanquake

contrib/bitcoin-qt.pro

@@ -22,8 +22,6 @@ cd src/
 make translate
 ```
 
-`contrib/bitcoin-qt.pro` takes care of generating `.qm` (binary compiled) files from `.ts` (source files) files. It’s mostly automated, and you shouldn’t need to worry about it.
-
 **Example Qt translation**
 ```cpp
 QToolBar *toolbar = addToolBar(tr("Tabs toolbar"));