Reverts 5b0d8f85fd.
Diagnostic producers can send diagnostics for buffers that are not
loaded, for which we cannot retrieve the line count to clamp line
numbers. This means that some diagnostics in the quickfix list could be
line-clamped and others not. The quickfix list can already handle line
numbers past the end of the buffer (i.e. it *already* clamps line
numbers) so just use the "raw" diagnostic positions sent from the
producer.
0341c687a3
