fix: remove test comment

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dd-david-levin

datafusion/sqllogictest/test_files/array.slt

@@ -8634,8 +8634,6 @@ SELECT string_to_array('', '')
 ----
 []
 
-# empty string with null_string arg — without the fix "".split(",") yields [""],
-# which is != the null_string "x", so the result would be [""] instead of []
 query ?
 SELECT string_to_array('', ',', 'x')
 ----