uucore: drop runtime branding env override; rely on automatic detection

Remove UUTILS_VERSION_BRAND runtime override path. Keep compile-time option_env! for packagers if needed. Tests updated to remove env override case; autoconf compatibility still validated via autoconf-like env hints. fmt/clippy/tests green.

Author: naoNao89

src/uucore/src/lib/lib.rs

@@ -343,11 +343,6 @@ fn get_runtime_brand() -> String {
         return brand.to_string();
     }
 
-    // Check for runtime environment variable override
-    if let Ok(brand) = env::var("UUTILS_VERSION_BRAND") {
-        return brand;
-    }
-
     // If likely under autoconf probe for mkdir, use GNU branding for compatibility
     if should_emit_gnu_brand() {
         return "GNU coreutils".to_string();
@@ -364,7 +359,7 @@ pub fn brand_version_static(brand: &'static str, version: &'static str) -> &'sta
 
 /// Generate version string with runtime autoconf detection
 pub fn runtime_version_string(_version: &'static str) -> &'static str {
-static VERSION_CACHE: LazyLock<String> = LazyLock::new(|| {
+    static VERSION_CACHE: LazyLock<String> = LazyLock::new(|| {
         let brand = get_runtime_brand();
         format!("({brand}) {}", env!("CARGO_PKG_VERSION"))
     });

tests/by-util/test_mkdir.rs

@@ -31,16 +31,6 @@ fn test_version_format_autoconf_compatibility() {
         .stdout_contains("(GNU coreutils)");
 }
 
-#[test]
-fn test_runtime_autoconf_detection_with_env_var() {
-    // Test explicit environment variable override
-    let mut cmd = new_ucmd!();
-    cmd.env("UUTILS_VERSION_BRAND", "GNU coreutils")
-        .arg("--version")
-        .succeeds()
-        .stdout_contains("(GNU coreutils)");
-}
-
 #[test]
 fn test_runtime_autoconf_detection_with_configure_env() {
     // Test autoconf environment variable detection