pt: export model_output_type instead of model_output_def

[njzjz]

Fix #3317.

[codecov]

Codecov Report

Attention: Patch coverage is 56.66667% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 75.29%. Comparing base (cf21b7a) to head (d251727).

Files	Patch %	Lines
deepmd/dpmodel/model/make_model.py	11.11%	8 Missing ⚠️
deepmd/pt/infer/deep_eval.py	28.57%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            devel    #3318   +/-   ##
=======================================
  Coverage   75.28%   75.29%           
=======================================
  Files         403      403           
  Lines       33888    33909   +21     
  Branches     1604     1604           
=======================================
+ Hits        25514    25531   +17     
- Misses       7513     7517    +4     
  Partials      861      861           

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