remove from "test_shock.py" redundant test functions for "magnitude" vs. "phase"

[CrepeGoat]

The tests in "test_shock.py" confirm the correctness of the shock spectra functions by validating the impulse responses for each function. Validation is currently performed by first confirming the impulse response's magnitude, which is generated by one set of functions, and then separately confirming the impulse response's phase, which is generated by a different set of functions.

This could be consolidated by combining the magnitude code and phase code for generation/validation, which would cut the number of test functions in half, w/o affecting the breadth of features being tested or increasing code complexity. The reduction in code size should make the tests easier to maintain.