[OpenMP] Remove `-Bsymbolic` flag for device linking in the GNU toolchain

[OpenMP] Remove `-Bsymbolic` flag for device linking in the GNU toolchain

Previously, OpenMP linking would be done explicitly in a linker stage.
For `x86_64` offloading this would just use the host linker, which could
be the `bfd` linker. This linker had problems linking relocations
against variables with protected visibility so we force `-Bsymbolic`
when linking. After the deprecation of the old offloading driver this
code is no longer used and can be removed.

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D136363