Make SST-1994m consistent with literature and use 2003m by default

[pcarruscag]

Proposed Changes

Remove divergence terms from the source term, use 2003m by default.

Related Work

Closes #1551

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.

[bigfooted]

Great work, looks like we are following the nasa website description of the model now, and the residuals did not change by a lot so that's comforting.