media: Make clearkeycdm a data_deps of media_unittests.
media: Make clearkeycdm a data_deps of media_unittests.

clearkeycdm target is needed by cdm_adapter_unittest.cc, but it's only loaded as a shared library, hence we should use data_deps [1, 2].

Without this CL, in GN build, I actually see a missing dependency even though
libclearkeycdm.so is built:

  out/GN/media_unittests: error while loading shared libraries: libclearkeycdm.so:
  cannot open shared object file: No such file or directory

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/media/cdm/ppapi/BUILD.gn&l=13

[2]
https://chromium.googlesource.com/chromium/src/+/master/tools/gn/docs/reference.md

BUG=584399
TEST=media_unittests now works in GN build.

Review URL: https://codereview.chromium.org/1667093003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#373759}

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