Clean up Sphere TimeDependentOptions

[knelli2]

Removes the ability to independently specify size coefficients because it wasn't used in practice. If we need to specify size coefficients we should do it from a file.

Proposed changes

Upgrade instructions

To use hard coded time dependent maps with the Sphere domain creator, you no longer specify the following option

  TimeDependentMaps:
    ...
    SizeMap:  # <-- Don't specify this
      InitialValues: [...]

Code review checklist

• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.
• The PR lists upgrade instructions and is labeled bugfix or
  new feature if appropriate.

Further comments

[knelli2]

@nilsvu Could you take a look at this? It's some prep to make #5541 simpler.

[nilsvu]

Add some upgrade instruction please