[AMDGPU][Libomptarget] Delete g_atl_machine global

With uses of g_atl_machine gone, a significant portion of dead
code has been removed.

This patch depends on D104691 and D104695.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D104696

GitOrigin-RevId: 9b8b7c1180eb3606fb08d2cdd9d6d18fae9cb2f5
10 files changed