EAMxx: upgrade/simplify step tendency calculation in atm procs #2997

Job	Run time
ci (ERS_Ld5_P4.ne4pg2_oQU480.F2010.ghci-oci_gnu.eam-wcprod_F2010)	20m 50s
ci (ERS_Ld5_P4.ne4pg2_oQU480.F2010-SCREAMv1-MPASSI.ghci-oci_gnu.eamxx-prod)	22m 33s
ci (ERS_P4.ne4pg2_oQU480.A.ghci-oci_gnu)	9m 9s
ci (SMS_D_Ln5_P4.ne4pg2_oQU480.F2010-SCREAMv1-MPASSI.ghci-oci_gnu)	21m 42s
ci (SMS_D_Ln5_P4.ne4pg2_oQU480.F2010.ghci-oci_gnu)	10m 46s
ci (ERS_P4.ne4pg2_oQU480.I1850ELMCN.ghci-oci_gnu.elm-qian_1948)	7m 15s
ci (SMS_D_Ln5_P4.ne4pg2_oQU480.F2010.ghci-oci_gnu)	10m 46s
ci (ERS_Ld5_P4.ne4pg2_oQU480.F2010.ghci-oci_gnu.eam-wcprod_F2010)	20m 50s
ci (ERS_Ld5_P4.ne4pg2_oQU480.F2010-SCREAMv1-MPASSI.ghci-oci_gnu.eamxx-prod)	22m 23s
ci (ERS_P4.ne4pg2_oQU480.I1850ELMCN.ghci-oci_gnu.elm-qian_1948)	7m 15s
ci (SMS_D_Ln5_P4.ne4pg2_oQU480.F2010-SCREAMv1-MPASSI.ghci-oci_gnu)	21m 42s
ci (ERS_P4.ne4pg2_oQU480.A.ghci-oci_gnu)	9m 9s
	3h 4m 20s

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