Clear redundant temp altitude/levels

[hazzas-99]

There are 2 use cases I can think of here:

1. When there is no APP/CTR top-down online, remove temp altitude for SIDs/SDRs/PDRs etc. (e.g. CC SANBA SID departs, no CC APP or North... picked up by Central who doesn't want to see A50)
2. When a controller drops a tag, and it is not assumed again within, say, 30 seconds, clear the temp altitude (e.g. KK LAM SID departs, South climbs to 190, Unicom... picked up by Scottish who doesn't want to see 190)

Potential other: if I pick up a departure from Dublin as North, and DW TWR hasn't cleared the 090 temp level, then the 090 is also irrelevant to me given the a/c is now climbing up to cruise... but might be more difficult to get this working without screwing something else over that I probably haven't thought of.

[AndyTWF]

All very do-able (though the last one is complicated!) will consider :)

[hazzas-99]

@AndyTWF just realised this is similar to #16

The last one is nowhere near essential, so if 1 and 2 are possible it'd be a godsend! 🙏