arm64: Back out "Use armhf cross-compiler for building compat vDSO"

This reverts the following Debian packaging commits:

 - 82c843e: [arm64] Use armhf cross-compiler for building compat vDSO
 - 26d1417: [arm64] Fix dependencies on armhf cross-compiler
 - d067319: [arm64] linux-headers: Disable check for a 32-bit compiler

since armhf cross-compiler is currently not available on arm64.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>