Remove apparently unnecessary Boostrap modules

sass/converse.scss

@@ -23,9 +23,6 @@
     @import "bootstrap/scss/input-group";
     @import "bootstrap/scss/custom-forms";
     @import "bootstrap/scss/nav";
-    @import "bootstrap/scss/navbar";
-    @import "bootstrap/scss/card";
-    @import "bootstrap/scss/breadcrumb";
     @import "bootstrap/scss/badge";
     @import "bootstrap/scss/alert";
     @import "bootstrap/scss/media";