Revert "dxfrw: leader based on unique_ptr"

This reverts commit 1c946bc8f1f6436ed152e3840eedec0e7525c780.
Revert "dxfrw: more fixing for potential memory leak"

This reverts commit 19c6b9e3759e6ecc36bbb935d7d637fa1ee24eda.
Revert "dxfrw: fixes for possible memory leak"

This reverts commit 313dac72c6681f741af25a86cb3b20c9aa2e5b9e.
SCM version 2.0.2
libdxfrw: fix mem_leak in drw_variant
libdxfrw: fix mem_leak in drw_header