Turn off methane in dynlakes test

I was getting a gridcell-level methane balance check error when running
ERS_Lm25.1x1_smallvilleIA.IHistClm50BgcCropQianRsGs.cheyenne_gnu.clm-smallville_dynlakes_monthly.
I'm thinking it was due to ESCOMP#43. So for now, I'm disabling
methane in this testmod. (I thought about changing it to an Sp case, but
(1) currently you're not allowed to run smallville in an Sp case, and
(2) it would be nice to exercise as much of the BGC code as possible in
this test, to exercise the dynamic landunit conservation code for BGC
variables.)

cime_config/testdefs/testmods_dirs/clm/smallville_dynlakes_monthly/user_nl_clm

@@ -7,3 +7,7 @@ do_transient_lakes = .true.
 ! Note that the use of this file means that this testmod can only be
 ! used with the 1x1_smallvilleIA grid.
 flanduse_timeseries = '$DIN_LOC_ROOT/lnd/clm2/surfdata_map/landuse.timeseries_1x1_smallvilleIA_hist_78pfts_simyr1850-1855_dynLakes_c200923.nc'
+
+! BUG(wjs, 2020-09-25, ESCOMP/CTSM#43) Dynamic lakes don't work when methane is active,
+! so for now disable methane for this test.
+use_lch4 = .false.

src/biogeochem/ch4Mod.F90

@@ -1251,7 +1251,7 @@ subroutine DynamicColumnAdjustments(this, bounds, clump_index, column_state_upda
     character(len=*), parameter :: subname = 'DynamicColumnAdjustments'
     !-----------------------------------------------------------------------
 
-    ! BUG(wjs, 2016-02-16, bugz 2283) Need to do some special handling of finundated for
+    ! BUG(wjs, 2016-02-16, ESCOMP/CTSM#43) Need to do some special handling of finundated for
     ! increases in lake area, since lakes are assumed to be 100% inundated. Probably it's
     ! most appropriate for this special handling to happen elsewhere - i.e., within this
     ! routine, we do the standard adjustments as they are currently done, but then in the