python3Packages.pydub: don't warn on calls to ffmpeg

The replacement was done in the codepath that is a fallback that
triggers a warning. So even though the library was ultimately calling to
the right nixpkgs binaries for ffmpeg tools, each call resulted in a
confusing warning like:

Couldn't find ffmpeg or avconv - defaulting to ffmpeg, but may not work

pkgs/development/python-modules/pydub/ffmpeg-fix-path.patch

@@ -1,28 +1,28 @@
 diff --git a/pydub/utils.py b/pydub/utils.py
-index 2694f90..7764b3f 100644
+index 740c500..e741100 100644
 --- a/pydub/utils.py
 +++ b/pydub/utils.py
-@@ -172,7 +172,7 @@ def get_encoder_name():
-     else:
-         # should raise exception
-         warn("Couldn't find ffmpeg or avconv - defaulting to ffmpeg, but may not work", RuntimeWarning)
+@@ -164,5 +164,5 @@ def get_encoder_name():
+     if which("avconv"):
+         return "avconv"
+-    elif which("ffmpeg"):
 -        return "ffmpeg"
++    elif which("@ffmpeg@"):
 +        return "@ffmpeg@"
-
-
- def get_player_name():
-@@ -186,7 +186,7 @@ def get_player_name():
      else:
-         # should raise exception
-         warn("Couldn't find ffplay or avplay - defaulting to ffplay, but may not work", RuntimeWarning)
+@@ -178,5 +178,5 @@ def get_player_name():
+     if which("avplay"):
+         return "avplay"
+-    elif which("ffplay"):
 -        return "ffplay"
++    elif which("@ffplay@"):
 +        return "@ffplay@"
-
-
- def get_prober_name():
-@@ -200,7 +200,7 @@ def get_prober_name():
      else:
-         # should raise exception
-         warn("Couldn't find ffprobe or avprobe - defaulting to ffprobe, but may not work", RuntimeWarning)
+@@ -192,5 +192,5 @@ def get_prober_name():
+     if which("avprobe"):
+         return "avprobe"
+-    elif which("ffprobe"):
 -        return "ffprobe"
++    elif which("@ffprobe@"):
 +        return "@ffprobe@"
+     else: