runtests: unset editor and pager related environment variables

Those environment variables could affect some configuration and future
tests. Drop them to avoid issues.

tests/run-tests.py

@@ -906,7 +906,7 b' class Test(unittest.TestCase):'
         env['TERM'] = 'xterm'
 
         for k in ('HG HGPROF CDPATH GREP_OPTIONS http_proxy no_proxy ' +
-                  'HGPLAIN HGPLAINEXCEPT ' +
+                  'HGPLAIN HGPLAINEXCEPT EDITOR VISUAL PAGER ' +
                   'NO_PROXY CHGDEBUG').split():
             if k in env:
                 del env[k]