Externals: remove PortAudio

Installer/dolphin-emu.spec

@@ -58,7 +58,6 @@ BuildRequires:  miniupnpc-devel
 BuildRequires:  openal-soft-devel
 #polarssl is now mbedtls:
 BuildRequires:  mbedtls-devel
-BuildRequires:  portaudio-devel
 BuildRequires:  SDL2-devel
 BuildRequires:  SFML-devel
 BuildRequires:  SOIL-devel
@@ -71,7 +70,6 @@ BuildRequires:  libSDL2-devel
 BuildRequires:  libSOIL-devel
 BuildRequires:  lzo-devel
 BuildRequires:  openal-devel
-BuildRequires:  portaudio-devel
 BuildRequires:  sfml-devel
 BuildRequires:  soundtouch-devel
 BuildRequires:  update-desktop-files