Fully-coupled compset has been renamed

[mnlevy1981]

Several test suites run

<test name="SMS_Ld2" grid="ne30pg3_t232" compset="BLT1850">

But that compset has been renamed B1850C_LTso as of cesm3_0_alpha07c. @gustavo-marques will open a PR with a fix for this (he is running the test suite from a clean sandbox for NCAR/MOM6#379)