Refactor: Remove the functions about pseudopotential from Unitcell.

[sunliang98]

Reminder

• Have you linked an issue with this pull request?
• Have you added adequate unit tests and/or case tests for your pull request?
• Have you noticed possible changes of behavior below or in the linked issue?
• Have you explained the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi? (ignore if not applicable)

Linked Issue

Fix #...

Unit Tests and/or Case Tests for my changes

• Update the corresponding Unit Tests.

What's changed?

• Remove read_pseudo and read_cell_pseudopots from Unitcell.
• Remove print_unitcell_pseudo from UnitCell.
• Delete module_cell/read_cell_pseudopots.cpp.

TODO:

• Remove the files about reading PP from module_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 ...