Address BMI header issues impeding other work

[PhilMiller]

Cf NOAA-OWP/ngen#831

Removals

• bmi/bmi.hxx header deleted
• #include "bmi/bmi.hxx" dropped since it wasn't actually used

Changes

• Modify bmi/bmi.h and include/bmi.h to define BMI_SUCCESS and BMI_FAILURE as const static int instead of #define macros, to avoid tripping over Macros BMI_SUCCESS and BMI_FAILURE prevent co-inclusion with C++ bmi-cxx/bmi.hxx csdms/bmi-c#12

Testing

1. CI

Notes

• This can get merged in advance of coordination with ngen#831 since it doesn't actually suffer from the ABI compatibility concern

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️