Remove stray dependencies in pdf/BUILD.gn.

- out_of_process_instance target doesn't use //base:i18n.
- internal target doesn't use //pdf/pdfium/fuzzers, but once that
  dependency gets removed, //pdf/pdfium/fuzzers is no longer in GN's
  build graph. Fix that by adding it to the "gn_all" target.

Change-Id: I811f085ce5666fcf353d2cb429e52a84e1fbd1f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2967774
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#894312}