Eliminate redundant check of index start against ctime

Eliminate redundant check of index start against ctime

When (the first version of) this check was added 10 years ago in
b4b4ef116880, it was presumably to ensure that "index; save; touch;
index" in the same second would flag a file as needing saving.

Since then, tmax has been added in the indexing process to solve the
problem by capping timestamps stored in the index. This capping means
that a file with ctime in the same second as an indexing start will
be picked up on both the indexes in the example above - there's no need
to special case the check.

Signed-off-by: Aidan Hobson Sayers <aidanhs@cantab.net>
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>