numfmt: use consistent debug warning format

Use the existing print_warning helper for the grouping-no-effect
message instead of a one-off writeln with util_name(). Use hardcoded
"numfmt:" prefix for the failed-to-convert message to match the other
debug warnings. Remove now-unused util_name import.

Author: sylvestre

src/uu/numfmt/src/numfmt.rs

@@ -20,8 +20,6 @@ use std::str::FromStr;
 use units::{IEC_BASES, SI_BASES};
 use uucore::display::Quotable;
 use uucore::error::UResult;
-use uucore::util_name;
-
 use uucore::i18n::decimal::locale_grouping_separator;
 use uucore::parser::shortcut_value_parser::ShortcutValueParser;
 use uucore::ranges::Range;
@@ -349,12 +347,7 @@ fn print_debug_warnings(options: &NumfmtOptions, matches: &ArgMatches) {
     }
 
     if options.grouping && locale_grouping_separator().is_empty() {
-        let _ = writeln!(
-            stderr(),
-            "{}: {}",
-            util_name(),
-            translate!("numfmt-debug-grouping-no-effect")
-        );
+        print_warning("numfmt-debug-grouping-no-effect");
     }
 
     // Warn if --header is used with command-line input
@@ -404,8 +397,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
             if options.debug && saw_invalid {
                 let _ = writeln!(
                     stderr(),
-                    "{}: {}",
-                    util_name(),
+                    "numfmt: {}",
                     translate!("numfmt-debug-failed-to-convert")
                 );
             }