[cc] Relax dependencies for //cc:cc

The //cc:cc component was directly depending on //components/ukm. This
is unnecessary since it really only needs to depend on
//services/metrics/public/mojom which it was inheriting via public_deps.

Having this unnecessary dependency causes the following dependency
chain:

  - //third_party/blink/public:blink_headers -->
  - //cc:cc -->
  - //components/ukm:ukm -->
  - <<hypothetical component that wants to look at blink_headers>> -->
  - //third_party/blink/public:blink_headers.

This relaxing the //cc to ///components/ukm dependency gives us more
flexibility in adding a new dependency to //components/ukm where such a
dependency itself is interested in blink_headers.

Bug: None
Change-Id: I71d19991b8068852cd06d31f79489012325980a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053148
Reviewed-by: Khushal <khushalsagar@chromium.org>
Commit-Queue: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741181}

• cc/BUILD.gn[diff]