gpu: Remove content/common/gpu DEPS
gpu: Remove content/common/gpu DEPS

With content/common/gpu moved to gpu/ipc/service, we can now get rid of the
DEPS file.

BUG=586385

Review URL: https://codereview.chromium.org/1870303002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#386424}

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