removed pythonpath construction from script

[AndrewEichmann-NOAA]

Effectively outsourced construction of what gets imported as the env variable PYTHONPATH to the environment. No changes were required in CMakeLists.txt because the necessary path construction was already there. So it's just removal of the additions to sys.path in scripts/exgdas_global_marine_analysis_prep.py.

Addresses issues #242 and #234 . Should break ctest test_gdasapp_soca_JGDAS_GLOBAL_OCEAN_ANALYSIS_PREP and dependencies until NOAA-EMC/global-workflow#1292 is merged.

[guillaumevernieres]

Yup, I think that should do it. Thanks @AndrewEichmann-NOAA .

[emcbot]

Automated GDASApp Testing Results:
Machine: hera

Start: Mon Jan 30 20:45:24 UTC 2023 on hfe10
---------------------------------------------------
Build:                                 *SUCCESS*
Build: Completed at Mon Jan 30 21:29:30 UTC 2023
---------------------------------------------------
Tests:                                 *SUCCESS*
Tests: Completed at Mon Jan 30 21:31:39 UTC 2023
Tests: 100% tests passed, 0 tests failed out of 28

[emcbot]

Automated GDASApp Testing Results:
Machine: orion

Start: Mon Jan 30 15:27:30 CST 2023 on Orion-login-1.HPC.MsState.Edu
---------------------------------------------------
Build:                                 *SUCCESS*
Build: Completed at Mon Jan 30 17:14:30 CST 2023
---------------------------------------------------
Tests:                                 *SUCCESS*
Tests: Completed at Mon Jan 30 17:19:09 CST 2023
Tests: 100% tests passed, 0 tests failed out of 28

[AndrewEichmann-NOAA]

@guillaumevernieres NOAA-EMC/global-workflow#1292 has been merged, so this should be safe