Clean up which/which-support Cargo feature (#5019)

* Rename "which" feature to "which-support"

* Ignore currently broken environment tests

crates/nu-command/src/core_commands/version.rs

@@ -256,7 +256,7 @@ fn features_enabled() -> Vec<String> {
         names.push("uuid".to_string());
     }
 
-    #[cfg(feature = "which")]
+    #[cfg(feature = "which-support")]
     {
         names.push("which".to_string());
     }