Remove arguments from internal functions where not required

[adisidev]

For example:

https://github.com/mgastner/cartogram-cpp/blob/cd878d8bd53c29f52c7b34a4548dd039c61f00cb/src/inset_state/integrate.cpp#L137

write_cairo_map accepts argument plot_grid. However, this is a command line argument. So, it should read this from within InsetState. If it is used differently (i.e. with false explicitly written) somewhere then reconsider. The ideal way would be we set it to default to the value from args_, and use a different value only if specified.

[adisidev]

Here is an example where I made the same change:
ae62aae