Disable ReadTheDocs build of PDF version of the docs

[gipert]

https://readthedocs.org/projects/pygama/builds/24552659/

There seems to be something wrong with this formula:

pygama/src/pygama/math/functions/step.py

Line 102 in ddd4414

pdf(x, \text{x_lo}, \text{x_hi}, \mu, \sigma, hstep) = pdf(y=\frac{x-\mu}{\sigma}, step, \text{x_lo}, \text{x_hi}) = \frac{1+hstep\text{erf}\left(\frac{x-\mu}{\sigma\sqrt{2}}\right)}{\sigma\left[(y-y_{min}) +hstep\left(y\text{erf}(\frac{y}{\sqrt{2}})+\sqrt{\frac{2}{\pi}}e^{-y^2/2}-y_{min}\text{erf}(\frac{y_{min}}{\sqrt{2}})+\sqrt{\frac{2}{\pi}}e^{-y_{min}^2/2}\right)\right]}

CC @SamuelBorden

[gipert]

Superseded by #588