remove underline from std NU_LOG_FORMAT (#10604)

# Description

This PR removes the underline from the log format. It's been messing
things up for me since there is no ansi reset in the log format and
therefore everything after it is underlined.

This PR should end things like this.

![image](https://github.com/nushell/nushell/assets/343840/17e6dc87-11ba-4395-aac3-f70872b9182a)


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crates/nu-std/std/log.nu

@@ -31,7 +31,7 @@ export-env {
         "DEBUG": "D"
     }
 
-    $env.NU_LOG_FORMAT = $"%ANSI_START%%DATE%|%LEVEL%|(ansi u)%MSG%%ANSI_STOP%"
+    $env.NU_LOG_FORMAT = $"%ANSI_START%%DATE%|%LEVEL%|%MSG%%ANSI_STOP%"
 
     $env.NU_LOG_DATE_FORMAT = "%Y-%m-%dT%H:%M:%S%.3f"
 }

crates/nu-std/tests/logger_tests/test_logger_env.nu

@@ -38,5 +38,5 @@ def env_log_short_prefix [] {
 
 #[test]
 def env_log_format [] {
-    assert equal $env.NU_LOG_FORMAT $"%ANSI_START%%DATE%|%LEVEL%|(ansi u)%MSG%%ANSI_STOP%"
+    assert equal $env.NU_LOG_FORMAT $"%ANSI_START%%DATE%|%LEVEL%|%MSG%%ANSI_STOP%"
 }