Do not build nacl_loader_unittests on the chromium.webkit Linux GN (dbg) bot.

This was broken in #326948; NaCl doesn't build in component debug yet ...

TBR=sigbornf@opera.com
BUG=

Review URL: https://codereview.chromium.org/1104913002

Cr-Commit-Position: refs/heads/master@{#326973}

testing/buildbot/chromium.webkit.json

@@ -465,7 +465,6 @@
       "mojo_public_system_unittests",
       "mojo_public_utility_unittests",
       "mojo_system_unittests",
-      "nacl_loader_unittests",
       "net_unittests",
       "ppapi_unittests",
       "printing_unittests",