Use envvar rather than nonstandard hint. lines

Use envvar rather than nonstandard hint. lines

The NOTES files have a bunch of hint lines that are removed when
generating LINT. However, we can achieve the same effect by prepending
each of the lines with 'envvar' so the NOTES files become standard
config(8) files. No functional changes as the sed script to generate
the LINT files filters these either way.

Suggested by: kevans