Revert "Move the rest of the sections over to DWARFContext."

This reverts commit r356682 because it breaks the DWO flavours of some
tests:
    lldb-Suite :: lang/c/const_variables/TestConstVariables.py
    lldb-Suite :: lang/c/local_variables/TestLocalVariables.py
    lldb-Suite :: lang/c/vla/TestVLA.py

llvm-svn: 356773