NaCl/GYP: remove references to prep_toolchain.

prep_toolchain is now a no-op.

BUG=456902

Review URL: https://codereview.chromium.org/1097153002

Cr-Original-Commit-Position: refs/heads/master@{#326044}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e9705fd6b87e9487773f58430aecc542e300911d
1 file changed