removed unused variables and added static cast to silence warnings

modules/conop/src/diag.cc

modules/geom/tests/test_transform.cc

modules/gfx/src/bitmap_io.cc

modules/gfx/src/exporter.cc

modules/gfx/src/impl/backbone_trace.cc

modules/gfx/src/impl/entity_detail.cc

modules/gfx/src/render_options/render_options.cc

modules/gui/src/python_shell/python_namespace_tree_item.cc

modules/gui/src/widget_geom_handler.cc

modules/img/base/tests/test_value_holder.cc

modules/io/pymod/export_mmcif_io.cc

modules/io/src/img/map_io_png_handler.cc

modules/io/src/mol/mmcif_reader.cc

modules/mol/alg/src/lddt.cc