Remove get_ functions

[jsallay]

We define several functions such as get_scalar, get_vector, etc. All of the classes already have a constructor that takes in a pmt that should be the same thing, with the same error checking. I don't think there is value is having: auto x = get_scalar<float>(p) vs auto x = scalar<float>(p). The second case requires less typing and is a little cleaner.

[jsallay]

@mormj Would this cause you any heartburn?

[mormj]

Not at all. Just a global search and replace from my perspective. Having less redundancy in the code is better!

[jsallay]

Removed some time ago.