RTM does not have the history_tape_in_use functionality #62

RTM and MOSART (unlike the CLM) do not have the history_tape_in_use functionality, so both models throw an error when h0i is empty. RTM and MOSART currently have at least one instantaneous field each, so that h0i will not be empty. If deemed necessary, we could refactor RTM and MOSART to include the history_tape_in_use functionality.

Applies to tags rtm1_0_87 and newer.

Relates to ESCOMP/MOSART#119.