Fix logically dead code

Logically dead code

The indicated dead code may have performed some action; that action will never occur. Code can never be reached because of a logical contradiction
/test/csuite/wt6616_checkpoint_oldest_ts/main.c:266: DEADCODE 116287 Assigning: "rand_time" = "false".
/test/csuite/wt6616_checkpoint_oldest_ts/main.c:276: DEADCODE 116287 Assigning: "rand_time" = "false".
/test/csuite/wt6616_checkpoint_oldest_ts/main.c:288: DEADCODE 116287 At condition "rand_time", the value of "rand_time" must be equal to 0.
/test/csuite/wt6616_checkpoint_oldest_ts/main.c:288: DEADCODE 116287 The condition "rand_time" cannot be true.
/test/csuite/wt6616_checkpoint_oldest_ts/main.c:289: DEADCODE 116287 Execution cannot reach this statement: "timeout = __wt_random(&rnd)...".