This reverts commit fc474e1069.
We don't have a concept of "complex infinity". But real infinity (of
any sign) is clearly a wrong answer here (it has well defined finite
phase and infinite absolute value), e.g.:
```pycon
>>> ellippi(1-1e-15, 1-1e-15j)
mpc(real='915673653288978.88', imag='-530451596311157.62')
>>> ellippi(1-1e-15, 1+1e-15j)
mpc(real='915673653288978.88', imag='530451596311157.62')
```
Closes#268
Sergey B Kirpichev
cd57adf8c7