Avoid isCellTTLExpired() for NO-TAG cases

As observed in this JIRA's performance test, we are always calling the isCellTTLExpired() for every cell and internally it is parsing the keyLength, valueLength() to get the tagsLength after which we decide whether Cell level TTL is present are not.

This JIRA aims to avoid this check if all the readers of the storescanner knows that there are no tags to read. Note that, for the memstore scanner we will do that in another JIRA, which I suppose Stack had already raised to avoid tag length while flushing (for the NO-TAG) case.