Delete dead code from the linker.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181094 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing header.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181095 91177308-0d34-0410-b5e6-96231b3b80d8
Remove unused members and constructor arguments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181096 91177308-0d34-0410-b5e6-96231b3b80d8
Don't store the context in the Linker.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181097 91177308-0d34-0410-b5e6-96231b3b80d8
Don't construct or delete a module on the Linker.

The linker is now responsible only for actually linking the modules, it
is up to the clients to create and destroy them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181098 91177308-0d34-0410-b5e6-96231b3b80d8