pdl: Remove public fields from lint::PacketScope

Remove group inlining in the linter, now performed in
the analyzer. Remove PacketScope members 'fields',
'constraints', which can now be derived from the
packet declaration itself.

Test: cargo test
Change-Id: Ic9bad86c0395b6e9315d2ed2d10e9f8640ea3648
Merged-In: Ic9bad86c0395b6e9315d2ed2d10e9f8640ea3648
(cherry picked from commit 1ff1141d)