dynamics: correct the definition of 'shearing strain rate' in comments

All occurences of 'shearing strain rate' as a comment before the
computation of the quantities `shear{n,s}{e,w}` define these quantities
as

    shearing strain rate  =  e_12

However, the correct definition of these quantities is 2*e_12.

Bring the code in line with the definition of the shearing strain rate
in the documentation (see the 'Internal stress' section in
doc/source/science_guide/sg_dynamics.rst), which defines

    D_S = 2\dot{\epsilon}_{12}

Correct these.

cicecore/cicedynB/dynamics/ice_dyn_eap.F90

@@ -1321,7 +1321,7 @@ subroutine stress_eap  (nx_block,   ny_block,       &
          tensionse = -cym(i,j)*uvel(i  ,j-1) - dyt(i,j)*uvel(i-1,j-1) &
                    +  cxp(i,j)*vvel(i  ,j-1) - dxt(i,j)*vvel(i  ,j  )
 
-         ! shearing strain rate  =  e_12
+         ! shearing strain rate  =  2*e_12
          shearne = -cym(i,j)*vvel(i  ,j  ) - dyt(i,j)*vvel(i-1,j  ) &
                  -  cxm(i,j)*uvel(i  ,j  ) - dxt(i,j)*uvel(i  ,j-1)
          shearnw = -cyp(i,j)*vvel(i-1,j  ) + dyt(i,j)*vvel(i  ,j  ) &

cicecore/cicedynB/dynamics/ice_dyn_evp_1d.F90

@@ -326,7 +326,7 @@ subroutine stress_i(NA_len, &
       ! tension strain rate  =  e_11 - e_22
       tensionne = -cym*uvel(iw) - dyt(iw)*tmp_uvel_ee                      &
                 +  cxm*vvel(iw) + dxt(iw)*tmp_vvel_se
-      ! shearing strain rate  =  e_12
+      ! shearing strain rate  =  2*e_12
       shearne = -cym*vvel(iw) - dyt(iw)*tmp_vvel_ee                        &
               -  cxm*uvel(iw) - dxt(iw)*tmp_uvel_se
       ! Delta (in the denominator of zeta, eta)
@@ -614,7 +614,7 @@ subroutine stress_l(NA_len, tarear, &
       tensionse = -cym*tmp_uvel_se - dyt(iw)*tmp_uvel_ne                  &
                 +  cxp*tmp_vvel_se - dxt(iw)*vvel(iw)
 
-      ! shearing strain rate  =  e_12
+      ! shearing strain rate  =  2*e_12
       shearne = -cym*vvel(iw) - dyt(iw)*tmp_vvel_ee                        &
               -  cxm*uvel(iw) - dxt(iw)*tmp_uvel_se
       shearnw = -cyp*tmp_vvel_ee + dyt(iw)*vvel(iw)                        &

cicecore/cicedynB/dynamics/ice_dyn_shared.F90

@@ -1165,7 +1165,7 @@ subroutine strain_rates (nx_block,   ny_block,   &
       tensionse = -cym(i,j)*uvel(i  ,j-1) - dyt(i,j)*uvel(i-1,j-1) &
                 +  cxp(i,j)*vvel(i  ,j-1) - dxt(i,j)*vvel(i  ,j  )
 
-      ! shearing strain rate  =  e_12
+      ! shearing strain rate  =  2*e_12
       shearne = -cym(i,j)*vvel(i  ,j  ) - dyt(i,j)*vvel(i-1,j  ) &
               -  cxm(i,j)*uvel(i  ,j  ) - dxt(i,j)*uvel(i  ,j-1)
       shearnw = -cyp(i,j)*vvel(i-1,j  ) + dyt(i,j)*vvel(i  ,j  ) &

cicecore/cicedynB/dynamics/ice_dyn_vp.F90

@@ -1695,7 +1695,7 @@ subroutine deformations (nx_block,   ny_block,   &
          tensionse = -cym(i,j)*uvel(i  ,j-1) - dyt(i,j)*uvel(i-1,j-1) &
                    +  cxp(i,j)*vvel(i  ,j-1) - dxt(i,j)*vvel(i  ,j  )
 
-         ! shearing strain rate  =  e_12
+         ! shearing strain rate  =  2*e_12
          shearne = -cym(i,j)*vvel(i  ,j  ) - dyt(i,j)*vvel(i-1,j  ) &
                  -  cxm(i,j)*uvel(i  ,j  ) - dxt(i,j)*uvel(i  ,j-1)
          shearnw = -cyp(i,j)*vvel(i-1,j  ) + dyt(i,j)*vvel(i  ,j  ) &
@@ -2605,7 +2605,7 @@ subroutine formDiag_step1  (nx_block,   ny_block,   &
          tensionse = -cym(i,j)*uij1  - dyt(i,j)*ui1j1 &
                    +  cxp(i,j)*vij1 - dxt(i,j)*vij
 
-         ! shearing strain rate  =  e_12
+         ! shearing strain rate  =  2*e_12
          shearne = -cym(i,j)*vij - dyt(i,j)*vi1j &
                  -  cxm(i,j)*uij - dxt(i,j)*uij1
          shearnw = -cyp(i,j)*vi1j + dyt(i,j)*vij &