Style: NGX_PTR_SIZE replaced with sizeof(void *).

The NGX_PTR_SIZE macro is only needed in preprocessor directives where
it's not possible to use sizeof().
diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index d2a8d01..cf665a4 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -410,7 +410,7 @@
                 hex = 2;
                 sign = 0;
                 zero = '0';
-                width = NGX_PTR_SIZE * 2;
+                width = 2 * sizeof(void *);
                 break;
 
             case 'c':