output/jack: remove DLL support

This effectively reverts commit 0f02bbc2fe which was a horrible
kludge for JACK support on Windows.  Maintaining this kludge doesn't
seem worth the trouble (the JACK version was never updated), and
apparently nobody uses this.

src/output/plugins/JackOutputPlugin.cxx

@@ -45,10 +45,6 @@ static constexpr unsigned MAX_PORTS = 16;
 
 static constexpr size_t jack_sample_size = sizeof(jack_default_audio_sample_t);
 
-#ifdef DYNAMIC_JACK
-#include "lib/jack/Dynamic.hxx"
-#endif // _WIN32
-
 class JackOutput final : public AudioOutput {
 	/**
 	 * libjack options passed to jack_client_open().
@@ -468,10 +464,6 @@ JackOutput::Disable() noexcept
 static AudioOutput *
 mpd_jack_init(EventLoop &, const ConfigBlock &block)
 {
-#ifdef DYNAMIC_JACK
-	LoadJackLibrary();
-#endif
-
 	jack_set_error_function(mpd_jack_error);
 
 #ifdef HAVE_JACK_SET_INFO_FUNCTION