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

[theweathermanda]

TYPE: Bug fix

KEYWORDS: seg fault, diag_nwp2

SOURCE: Menda Chasteen

DESCRIPTION OF CHANGES:
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.

LIST OF MODIFIED FILES:
dyn_em/start_em.F

TESTS CONDUCTED:
The regression tests are all passing.

RELEASE NOTE: This PR fixes a seg fault error due to early deallocation of array dz8w for diag_nwp2=2 option in start_em.F.

[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

[islas]

@theweathermanda Could you update your PR description to use the PR template?

[weiwangncar]

@theweathermanda I modified your PR message. Please see if there is anything you would like to change.