Remove the concept of having more than one course export format tagged.

...contentstore/management/commands/export_convert_format.py

...e/management/commands/tests/test_export_convert_format.py

common/lib/xmodule/xmodule/modulestore/xml_exporter.py

common/lib/xmodule/xmodule/tests/data/EmptyCourse.tar.gz

common/lib/xmodule/xmodule/tests/data/NoVersionNumber.tar.gz

common/lib/xmodule/xmodule/tests/data/Version0_drafts.tar.gz

...n/lib/xmodule/xmodule/tests/data/Version0_nodrafts.tar.gz

common/lib/xmodule/xmodule/tests/data/Version1_drafts.tar.gz

...le/xmodule/tests/data/Version1_drafts_extra_branch.tar.gz

...n/lib/xmodule/xmodule/tests/data/Version1_nodrafts.tar.gz

...ib/xmodule/xmodule/tests/data/Version1_nopublished.tar.gz

common/lib/xmodule/xmodule/tests/test_export.py