spotify: Fix GStreamer warning on seek (fixes #227)
spotify: Fix GStreamer warning on seek (fixes #227)

Don't call audio.{prepare_change,start_playback}() before/after seek. This does
not seem to have any effect on functionality, and avoids Gstreamer failing to
disconnect the "notify::source" signal handler, which again causes a warning.

jmarsik/mopidy,glogiotatidis/mopidy,jcass77/mopidy,diandiankan/mopidy,kingosticks/mopidy,jmarsik/mopidy,vrs01/mopidy,glogiotatidis/mopidy,mopidy/mopidy,liamw9534/mopidy,jodal/mopidy,bacontext/mopidy,bencevans/mopidy,tkem/mopidy,ali/mopidy,mopidy/mopidy,woutervanwijk/mopidy,jcass77/mopidy,vrs01/mopidy,pacificIT/mopidy,tkem/mopidy,jodal/mopidy,hkariti/mopidy,jmarsik/mopidy,SuperStarPL/mopidy,pacificIT/mopidy,bacontext/mopidy,woutervanwijk/mopidy,priestd09/mopidy,glogiotatidis/mopidy,dbrgn/mopidy,ali/mopidy,adamcik/mopidy,kingosticks/mopidy,vrs01/mopidy,diandiankan/mopidy,ZenithDK/mopidy,tkem/mopidy,diandiankan/mopidy,tkem/mopidy,quartz55/mopidy,mokieyue/mopidy,hkariti/mopidy,dbrgn/mopidy,bencevans/mopidy,diandiankan/mopidy,swak/mopidy,mokieyue/mopidy,quartz55/mopidy,kingosticks/mopidy,pacificIT/mopidy,SuperStarPL/mopidy,priestd09/mopidy,rawdlite/mopidy,mopidy/mopidy,abarisain/mopidy,jcass77/mopidy,swak/mopidy,pacificIT/mopidy,adamcik/mopidy,quartz55/mopidy,ali/mopidy,SuperStarPL/mopidy,vrs01/mopidy,swak/mopidy,glogiotatidis/mopidy,rawdlite/mopidy,dbrgn/mopidy,priestd09/mopidy,ali/mopidy,rawdlite/mopidy,liamw9534/mopidy,SuperStarPL/mopidy,abarisain/mopidy,hkariti/mopidy,bencevans/mopidy,rawdlite/mopidy,quartz55/mopidy,swak/mopidy,adamcik/mopidy,hkariti/mopidy,dbrgn/mopidy,jmarsik/mopidy,mokieyue/mopidy,ZenithDK/mopidy,bacontext/mopidy,ZenithDK/mopidy,ZenithDK/mopidy,jodal/mopidy,mokieyue/mopidy,bacontext/mopidy,bencevans/mopidy