Obsolete comment in CopyReadLineText()

CopyReadLineText quoth:

* The objective of this loop is to transfer the entire next input line
* into line_buf. Hence, we only care for detecting newlines (\r and/or
* \n) and the end-of-copy marker (\.).
*
* In CSV mode, \r and \n inside a quoted field are just part of the data
* value and are put in line_buf. We keep just enough state to know if we
* are currently in a quoted field or not.
*
* These four characters, and the CSV escape and quote characters, are
* assumed the same in frontend and backend encodings.

When that last bit was written, it was because we were detecting
newlines and end-of-copy markers before performing encoding
conversion. That's not true any more: by the time CopyReadLineText
sees the data, it was already converted by CopyConvertBuf. So
I don't believe there actually is any such dependency anymore,
and we should simply remove that last sentence. Any objections?

regards, tom lane