[Remove] remove BasicStringPiece in comments

Signed-off-by: mwish <anmmscs_maple@qq.com>

src/butil/strings/string_piece.h

@@ -155,7 +155,7 @@ BUTIL_EXPORT StringPiece16 substr(const StringPiece16& self,
 
 // Defines the types, methods, operators, and data members common to both
 // StringPiece and StringPiece16. Do not refer to this class directly, but
-// rather to BasicStringPiece, StringPiece, or StringPiece16.
+// rather to StringPiece, or StringPiece16.
 //
 // This is templatized by string class type rather than character type, so
 // BasicStringPiece<std::string> or BasicStringPiece<butil::string16>.