AK: Remove StringBuilder::build() in favor of to_deprecated_string()

Having an alias function that only wraps another one is silly, and
keeping the more obvious name should flush out more uses of deprecated
strings.
No behavior change.

Meta/Lagom/Tools/CodeGenerators/LibLocale/GenerateRelativeTimeFormatData.cpp

@@ -150,7 +150,7 @@ static ErrorOr<void> parse_all_locales(DeprecatedString dates_path, CLDR& cldr)
         if (auto region = cldr.unique_strings.get(parsed_locale.region); !region.is_empty())
             builder.appendff("-{}", region);
 
-        return builder.build();
+        return builder.to_deprecated_string();
     };
 
     while (dates_iterator.has_next()) {