Remove microbes from SIPNET

[dlebauer]

Minimum requirement is to throw error when ctx.microbes = 1; the rest is cleaning up the code.

Rationale:

• MICROBES is confusing and, as noted in microbeC, litter and litterWater are constant in niwot.out test #111, it is not clear if it behaves as intended.
• Zobitz et al. (2008) found that microbial and litter-quality structure is not identifiable from NEE, and did not support for retaining an abstract microbial or “litter quality” pool. It is possible that this could be constrained with R_H, but current behavior is unverified and structure is abstract.
• A nitrogen cycle is mostly implemented. If future work wants to explore microbial dynamics, it wouldn't be parsimonious (in the simple approach of SIPNET) to have an abstract 'quality' concept that is independent of C:N.

Proposed action:

• Deprecate and remove MICROBES (and associated litter-quality logic).
• If ctx.microbes = 1, fail fast with a clear error.
• Leave consideration of a microbial component to future work; there is no current work proposing to use microbes.

[ayushman1210]

hi @dlebauer i would like to work on this issue please assign it to me thanks !!