Moved deallocate statement: error when setting diag_nwp2 = 1 due to memory deallocation

[theweathermanda]

Running with diag_nwp2 = 1 leads to a segmentation fault related to prematurely deallocating dz8w in start_em.F.

This PR fixes the error by moving the deallocate statement to after the trad_fields call

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None