snapdragon: cross snap build broken

SRU Justification

Impact:
    snap cross building is broken and snap package can only build natively
    additionally snapcraft.yaml is using deprecated scriptlet syntax for install overrides
    this syntax has been deprecated by snapcraft and should be replaced with new one to future proof builds

Step to reproduce:
 - cross build with snapcraft on x86_64 host by calling: snapcraft --targer-arch=arm64

Expected result:
 snap package builds without warnings

Actual result:
 build fails

TEST CASE:
 - cross build with snapcraft on x86_64 host by calling: snapcraft --targer-arch=arm64
 - build should complete without errors and snapcraft warnings