[lldb] Don't delete orphaned shared modules in SBDebugger::DeleteTarget

In D83876 the consensus seems that LLDB should never deleted orphaned modules
implicitly. However, SBDebugger::DeleteTarget is currently doing exactly that.
This code was added in 75340622 but I don't see
any explanation in the commit, so I think we should delete it.

Reviewed By: clayborg

Differential Revision: https://reviews.llvm.org/D83933