`beta` not capable of handling `wminkowski`, `mahalanobis`

[ChrisKeefe]

Bug Description Beta diversity calculations using these two metrics fail. wminkowski takes an extra parameter, and has been deprecated in favor of the "weighted version of minkowski". mahalanobis produces a numpy.linalg.LinAlgError: Singular Matrix error, when handed any of a number of frequently-used test-data sets (crawford, moving pictures, and a minimal example).

Steps to reproduce the behavior

1. Load a qiime2 env, and run:

   qiime diversity beta \
   --i-table table.qza \
   --p-metric <insert-metric-here> \
   --o-alpha-diversity <metric-name>.qza

   passing a valid feature table. See the resulting error message.

Computation Environment

• OS: linuxMint 19.3
• QIIME 2 2020.6

Approach

• Replace wminkowski with minkowski, opening an issue to suggest handling of the weighted version in future
• Remove mahalanobis for now, and open a second issue to track replacement.