Don't copy libportaudio-2.dll anymore

Our MSYS dependencies have stopped depending on this
so it's disappeared from our environment.
We don't need to copy it anymore.

CMakeLists.txt

@@ -171,7 +171,6 @@ else()
     find_windows_dll(MODPLUG_DLL "libmodplug-1.dll")
     find_windows_dll(OPUSFILE_DLL "libopusfile-0.dll")
     find_windows_dll(OPUS_DLL "libopus-0.dll")
-    find_windows_dll(PORTAUDIO_DLL "libportaudio-2.dll")
     find_windows_dll(READLINE_DLL "libreadline8.dll")
     find_windows_dll(SNDFILE_DLL "libsndfile-1.dll")
     find_windows_dll(VORBISENC_DLL "libvorbisenc-2.dll")
@@ -636,7 +635,6 @@ if(WIN32 AND NOT MSVC)
     target_copy_file(librwe ${OPUSFILE_DLL}) # MSYS2 SDL2_mixer depends on opusfile
     target_copy_file(librwe ${SSP_DLL}) # MSYS2 SDL2_mixer libflac depends on ssp
     target_copy_file(librwe ${OPUS_DLL})
-    target_copy_file(librwe ${PORTAUDIO_DLL})
     target_copy_file(librwe ${READLINE_DLL})
     target_copy_file(librwe ${SNDFILE_DLL})
     target_copy_file(librwe ${VORBISENC_DLL})