signal.__init__.py: remove duplicated get_window entry

[megies]

For a moment I was a bit confused about a duplicated mention of get_window routine(s) (with different description) in the overview of scipy.signal (i.e. in scipy.signal.__init__.py docstring). So for a moment I was concerned about a possible name clash, especially because I stumbled over this trying to restore backwards compatibility in our code (regarding the "new" signal.windows submodule).

I think it should be avoided to mention the routine (it seems there never was a different routine with the same name) twice in two different sections.

I'm basing this on master being a bit unsure whether it should rather be based on the current maintanance branch..

[coveralls]

Coverage remained the same when pulling 3c5e59c on megies:signal_docstring_get_window into 6f9b0a7 on scipy:master.

[pv]

Thanks, seems fine