branches/zip: struct mtr_struct: Remove the unused field magic_n

unless UNIV_DEBUG is defined.  mtr->magic_n is only assigned to
and checked in UNIV_DEBUG builds.

include/mtr0mtr.h

@@ -344,10 +344,14 @@ struct mtr_struct{
 				this mtr */
 	ib_uint64_t	end_lsn;/* end lsn of the possible log entry for
 				this mtr */
+#ifdef UNIV_DEBUG
 	ulint		magic_n;
+#endif /* UNIV_DEBUG */
 };
 
-#define	MTR_MAGIC_N		54551
+#ifdef UNIV_DEBUG
+# define MTR_MAGIC_N		54551
+#endif /* UNIV_DEBUG */
 
 #define MTR_ACTIVE		12231
 #define MTR_COMMITTING		56456

include/mtr0mtr.ic

@@ -28,10 +28,9 @@ mtr_start(
 	mtr->modifications = FALSE;
 	mtr->n_log_recs = 0;
 
-#ifdef UNIV_DEBUG
-	mtr->state = MTR_ACTIVE;
-	mtr->magic_n = MTR_MAGIC_N;
-#endif
+	ut_d(mtr->state = MTR_ACTIVE);
+	ut_d(mtr->magic_n = MTR_MAGIC_N);
+
 	return(mtr);
 }