[Poetry][HOC] Only set poem state for poetry_hoc levels

[ajpal]

reported via slack thread

If there's no poem dropdown, we don't want to set the poem state even if the user somehow has a poem set in their progress or the level has a default poem. When there's no poem dropdown, the poem must be set using blocks.

[maddiedierker]

i think we should clear default_poem from the level when the state changes in levelbuilder rather than explicitly checking the standalone app before setting a poem