Remove duplicate build entry for HarfBuzz.

The Chromium build system doesn't generally care, but warnings pop up in
several ides when projects have duplicate source files.

Change-Id: I4f747246dde1736799f85faa4ae97c0bf6eb8b7e
Reviewed-on: https://chromium-review.googlesource.com/c/1459036
Commit-Queue: Ben Wagner <bungeman@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630057}

third_party/harfbuzz-ng/BUILD.gn

@@ -101,7 +101,6 @@ if (use_system_harfbuzz) {
       "src/src/hb-ot-hmtx-table.hh",
       "src/src/hb-ot-kern-table.hh",
       "src/src/hb-ot-layout-base-table.hh",
-      "src/src/hb-ot-layout-base-table.hh",
       "src/src/hb-ot-layout-common.hh",
       "src/src/hb-ot-layout-gdef-table.hh",
       "src/src/hb-ot-layout-gpos-table.hh",