Removing the requirement of "aligned" attribute support.

Before 0a2a0b5a74f4, the address of values used in runtime had to be the
multiple of 16, because the address of a variable was used as its VM
index. The first 4 bits of an index signified the scope of a varible.

This is no longer the case, after 0a2a0b5a74f4 the address of a variable
is never used as its VM index.
diff --git a/src/njs_value.h b/src/njs_value.h
index 28aed7e..b3049d2 100644
--- a/src/njs_value.h
+++ b/src/njs_value.h
@@ -105,10 +105,6 @@
 typedef struct njs_object_init_s      njs_object_init_t;
-#error "aligned attribute is required"
 union njs_value_s {
      * The njs_value_t size is 16 bytes and must be aligned to 16 bytes