[Libomptarget] Revert changes to AMDGPU plugin destructors

These patches exposed a lot of problems in the AMD toolchain. Rather
than keep it broken we should revert it to its old semi-functional
state. This will prevent us from using device destructors but should
remove some new bugs. In the future this interface should be changed
once these problems are addressed more correctly.

This reverts commit ed0f2181.

This reverts commit 2b7203a3.

Fixes #57536

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D133997