Remove MINERvA-specific code/classes (and add to MAT-MINERvA)

[bamesserly]

Several classes in this repo have dependencies on classes that belong in MAT-MINERvA. As a band-aid solution, we moved those MAT-MINERvA classes back into this repo. But sooner rather than later we need to separate the dependencies and move the MINERvA classes back to their own repo.

In most cases, we need to perform open-heart surgery to extricate them. In other places (e.g. MnvH3D), the classes just need to be removed altogether. And there are other cases (e.g. HyperDimLinearizer) where the classes belong in this repo, but got added to MAT-MINERvA.

These classes should be removed from this repo and added to MAT:

• FluxReweighter
• FluxSystematics
• MnvFluxConstraint
• MnvColors

And these classes should be removed from this repo (and MAT-MINERvA for that matter) altogether:

• MnvH3D
• MnvVertErrorBand3D
• MnvLatErrorBand
• MnvLatErrorBand2D
• MnvLatErrorBand3D

Return to this repo from MAT-MINERvA:

• HyperDimLinearizer
• PhysicsVariables

[bamesserly]

The macros and scripts directories also need to be organized.

[bamesserly]

Removing the code that I have already removed is not so simple bc UnfoldUtils depends on it.