patch 8.1.1529: libcanberra is linked with even when not used

Problem:    Libcanberra is linked with even when not used.
Solution:   Have configure check for libcanberra only when wanted.
            (suggestions by Libor Bukata)
diff --git a/src/feature.h b/src/feature.h
index c5d7d77..eb474ab 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -663,7 +663,7 @@
 /*
  * sound - currently only with libcanberra
  */
-#if !defined(FEAT_SOUND) && defined(FEAT_BIG) && defined(HAVE_CANBERRA)
+#if !defined(FEAT_SOUND) && defined(HAVE_CANBERRA)
 # define FEAT_SOUND
 #endif