integration of math_eqref_format with numref_format, and math_numfig with numfig.

[tk0miya]

Problem

• In Fix #4333: Enable directives and roles for math by default #4975, math directives and roles are integrated to sphinx-core.
• After the change, we can integrate math_eqref_format with numref_format, and math_numfig and numfig.
• We should discuss to do or not to do that.