Remove BFBFLAG from our testing

[ekluzek]

With NUOPC/CMEPS the BFBFLAG XML variable no longer does anything. As such it should be removed from our testing.

Here are the instances of it I see now:

testdefs/testlist_clm.xml:      <option name="comment">Can use this test to determine if there are significant throughput changes, at least for this common and important configuration. Note that this deliberately doesn't have any testmods in order to (1) avoid doing history output (because the timing of output can be very variable, and mixing output timing with other aspects of model time can be confusing), and (2) generally keep the test replicating a production configuration as closely as possible (so, for example, we do NOT set BFBFLAG=TRUE for this test).</option>
testdefs/testmods_dirs/clm/Fates/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/FatesColdAllVars/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/FatesColdBasic/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/basic/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/cmip6_deck/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/datm_bias_correct_cruv7/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/irrigOn_reduceOutput/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/nofire/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/rad_hrly_light_res_half/shell_commands:./xmlchange BFBFLAG="TRUE"
testdefs/testmods_dirs/clm/reduceOutput/shell_commands:./xmlchange BFBFLAG="TRUE"