Elemental Si not conserved in `get_total_amount()` after equilibration

[SuixiongTay]

Description

After calling equilibrate(), the get_total_amount("Si") returns double the input concentration. This is relevant to a fix from a previous bug.

Reproducible example

s1=Solution({"Si+4": "0.02 mol/L", "Cl-": "0.02 mol/L"}, balance_charge=None)
s1.equilibrate()
assert np.isclose(s1.get_total_amount("Si", 'mol/L').magnitude, 0.02), s1.get_total_amount("Si", 'mol/L').magnitude

#AssertionError: 0.03999888940384343

We should expect the get_total_amount for elemental Si to be conserved at 0.02 mol/L regardless of speciation. The bug may be an odd case of double counting for both the input and equilibrated Si species.