(partially) Fix Bug#55227 Fix compiler warnings in innodb with gcc 4.6

Fix compiler warning:
./include/ut0rnd.ic: In function 'ut_rnd_gen_ulint':
./include/ut0rnd.ic:88:8: error: variable 'n_bits' set but not used [-Werror=unused-but-set-variable]

storage/innodb_plugin/include/ut0rnd.ic

@@ -85,9 +85,6 @@ ut_rnd_gen_ulint(void)
 /*==================*/
 {
 	ulint	rnd;
-	ulint	n_bits;
-
-	n_bits = 8 * sizeof(ulint);
 
 	ut_rnd_ulint_counter = UT_RND1 * ut_rnd_ulint_counter + UT_RND2;