Fix latent bug of incorrectly providing header_start in NoHeader reader

The call to read GOES 5-min X-ray data contained a header keyword argument `header_start=3`:
```
dat = ascii.read(urldat, guess=False, Reader=ascii.NoHeader,
                     data_start=3, header_start=3, names=colnames)
```
This is incorrect and causes `ascii.read` to actually read the 3rd data line as the header initially before changing the column names to `colnames`.  In astropy 0.2.1 this accidentally worked, but in astropy 0.3 (installed Dec 20, 2013) this causes an error "duplicate column names" if any of the data values are identical.  The first time this happened was on Jan. 1 because the month is 1 and the day is 1.

Note, in astropy 0.4, specifying `header_start` in this situation will raise an exception.