remove: remove math/base/ops/add4

This commit removes `@stdlib/math/base/ops/add4` in favor of
`@stdlib/number/float64/base/add4`.

BREAKING CHANGE: remove `math/base/ops/add4`

To migrate, users should update their require/import paths to use
`@stdlib/number/float64/base/add4` which provides the same API and
implementation.

Ref: #2261

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Author: gururaj1512