Remove LegacyPlayerView reference from comment in proguard-rules.txt

This class is deprecated (and will be removed from media3).

#minor-release

PiperOrigin-RevId: 426860018

library/ui/proguard-rules.txt

 # Proguard rules specific to the UI module.
 
-# Constructor method accessed via reflection in StyledPlayerView and PlayerView
+# Constructor method accessed via reflection in StyledPlayerView
 -dontnote com.google.android.exoplayer2.video.spherical.SphericalGLSurfaceView
 -keepclassmembers class com.google.android.exoplayer2.video.spherical.SphericalGLSurfaceView {
   <init>(android.content.Context);