[iwyu] Removed unneeded excludes

These two headers can be included in isolation currently, so no need to
exclude them.

R=marja@chromium.org

Bug: v8:7965
Change-Id: I6250a237e6884bc3f89e666bca5d8f4129472fe6
Reviewed-on: https://chromium-review.googlesource.com/c/1303715Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57056}

tools/generate-header-include-checks.py

@@ -36,8 +36,6 @@ AUTO_EXCLUDE = [
   'src/dateparser-inl.h',
   'src/ic/ic.h',
   'src/lookup.h',
-  'src/parsing/parser.h',
-  'src/parsing/preparser.h',
   'src/regexp/jsregexp.h',
   'src/snapshot/object-deserializer.h',
   'src/transitions.h',