sstables: Don't validate timestamps against the max value on parsing.
sstables: Don't validate timestamps against the max value on parsing.

Internally, timestamps are represented as signed integers (int64_t) but
stored as unsigned ones. So it is quite possible to store data with
timestamp that is represented as a number larger than the max value of
int64_t type.
One such example is api::min_timestamp() that is used when generating
system schema tables ("keyspaces"). When cast to uint64_t, it turns into
a large value.

Signed-off-by: Vladimir Krivopalov <dc9186a06078733915a6fcbab34e59120be2b484@scylladb.com>

scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla