Remove UPX recommendation in Optimizing for size

The downsides (such as false positives in antivirus programs)
are usually not worth the upsides.

Moreover, when distributing a game using a platform like Steam,
SteamPipe will compress the data that will be sent to the player
downloading the game, even if the original game data is uncompressed.

development/compiling/optimizing_for_size.rst

@@ -151,18 +151,3 @@ If you build from source, remember to strip debug symbols from binaries:
 ::
 
     strip godot.64
-
-Using UPX to compress binaries
-------------------------------
-
-If you are targeting desktop platforms, the
-`UPX <https://upx.github.io/>`_ compressor can be used.
-This can reduce binary size considerably.
-
-.. warning::
-
-    You cannot use embedded PCK files with UPX compression.
-
-However, keep in mind that some antivirus programs may detect UPX-packed
-binaries as a virus. Therefore, if you are releasing a commercial game,
-make sure to sign your binaries or use a platform that will distribute them.