Signature header reservation not getting used

[pmatilai]

Commit 1847fd6 broke the signature header reservation usage when signing, it doesn't appear to be used at all now. There appeared to be issues with it before that too though.

We never had any tests for that thing so it's not really surprising...

[bmwiedemann]

related: with 4.20.1, --delsign reduces package size by 1104 bytes, while it is supposed to just reset the reserved space to 0.

[pmatilai]

@bmwiedemann, that's another issue. See the discussion in #2965, but the short version is that rpmsign can not know the original state of a package and thus cannot restore it reliably.