Remove duplicate insert function declaration

Remove extraneous insert signature

Author: TylerMSFT

docs/standard-library/basic-string-class.md

@@ -2959,9 +2959,6 @@ basic_string<CharType, Traits, Allocator>& insert(
     size_type count,
     value_type char_value);
 
-iterator insert(
-    iterator iter);
-
 iterator insert(
     iterator iter,
     value_type char_value);