Remove a few sage.xyz.all imports, so that the whole module xyz.all doesn't need to be loaded. That's not so important for the normal usage of sage, as there sage.all loads these other all imports as well. But this gets more important when part of sage is used as a library, and for the upcoming modularization.

Also two unused imports are removed.
The other changes are cosmetic (from ... import).

CC: @mkoeppe

Component: refactoring

Author: Tobias Diez

Branch/Commit: 875ba9e

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/30715