Remove getmodel and setmodel after transferred to DynamicPPL

[sunxd3]

ref TuringLang/DynamicPPL.jl#626

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.65%. Comparing base (29a1342) to head (1f075fd).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2292      +/-   ##
==========================================
- Coverage   85.82%   85.65%   -0.18%     
==========================================
  Files          24       24              
  Lines        1623     1617       -6     
==========================================
- Hits         1393     1385       -8     
- Misses        230      232       +2     

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[coveralls]

Pull Request Test Coverage Report for Build 10038735101

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 85.989%

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Totals
Change from base Build 9953741319:	-0.05%
Covered Lines:	1387
Relevant Lines:	1613

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💛 - Coveralls