Clean up the code to remove the original `simxDfoo()` functions

[gavinsimpson]

Now that coenocline() exists as the general interface to simulating from any of the stated response models and random deviate-generating distributions there is no need for these early functions.

Remove code and Rd pages for:

• sim1dPoisson()
• sim2dPoisson()
• sim1dNegbin()
• sim2dNegbin()
• sim1dBinom()
• sim2dBinom()
• sim1dBeta()

Also remove

• gaussianResponse()
• biGaussianResponse()
• betaResponse()

and any associated unit tests.

Also remove from R/expand.R

• expandGaussian()
• expandBeta()

[gavinsimpson]

The series of commits above completes the removal of this old code that is no longer needed after being superseded by coenocline().