Replace temporary ccpp_const_get_idx subroutine with official CCPP-framework version

[nusbaume]

Now that NCAR/ccpp-framework#622 has been merged, the CCPP-framework itself provides a mechanism to look up a constituent array index based off the standard name(s). This provides an opportunity to replace the temporary ccpp_const_get_idx subroutine in to_be_cccppized/ccpp_const_utils.F90 with an official framework version, which will inherit all of the associated benefits (more easily portable, better tested, etc.).

Note that this will require an update to CAM-SIMA as well, both to update the framework tag to access the new routine, and to replace the use of ccpp_const_get_idx in CAM-SIMA itself.