Refactor: Remove useless variables from read_pp.h.

[sunliang98]

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Linked Issue

Fix #...

Unit Tests and/or Case Tests for my changes

• Update corresponding unit test.

What's changed?

• Now Pseudopot_upf will read in the data and save them into Atom_pseudo directly, not save in itself.

This is the first step to refactor the pseudopotential part. Next, we will remove the function read_pseudo from cell, and then remove all the things about pseudopotential from cell.

Any changes of core modules? (ignore if not applicable)

• Example: I have added a new virtual function in the esolver base class in order to ...