[clang][driver] Remove dynamic gcc-toolset/devtoolset logic

This breaks when the newest available devtoolset directory is not a
complete toolset: https://github.com/llvm/llvm-project/issues/57843

Remove this again in favor or just adding the two new directories for
devtoolset/gcc-toolset 12.

This reverts commit 35aaf548.
This reverts commit 9f977202.

Fixes https://github.com/llvm/llvm-project/issues/57843

Differential Revision: https://reviews.llvm.org/D136435