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.

Userland/Libraries/LibC/time.cpp

@@ -390,7 +390,7 @@ size_t strftime(char* destination, size_t max_size, char const* format, const st
             return 0;
     }
 
-    auto str = builder.build();
+    auto str = builder.to_deprecated_string();
     bool fits = str.copy_characters_to_buffer(destination, max_size);
     return fits ? str.length() : 0;
 }