Remove dev.pl

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Faster parsing of RFC 3339 timestamps

The old code was fun because its implementation relied solely on the
constraint solver to find solutions.  Unfortunately, it was needlessly
slow.  Instead, we fall back to form_time/2 and parse_time/3 which give
us epoch seconds directly.  We can convert that into a datetime value
very quickly.

The old code required 7.2 million inferences to parse 100 timestamps.
The new code requires 32 thousand.  That's two orders of magnitude
faster.

The downside is that parse_time/3 doesn't support fractional seconds.
Ideally we would support full nanosecond precision when parsing RFC 3339
timestamps.  At some point, I'll submit a patch to SWI-Prolog so that
parse_time/3 does the right thing in that case.  Then we'll be fixed
too.