Subzero: Remove the GlobalContext::GlobalDeclarations vector.

Subzero: Remove the GlobalContext::GlobalDeclarations vector.

Elements were added to this vector, but never inspected, so it is
essentially a useless field.  Plus, the removal allows us to remove a
couple of friend declarations.

BUG=none
R=kschimpf@google.com

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=a086b9135f3a492100ab349a5dccad8a1599f4bd

[Jim Stichnoth, 2015-01-20 21:57:52]

stichnot@chromium.org changed reviewers:
+ jvoung@chromium.org, kschimpf@google.com

[Karl, 2015-01-20 22:00:08]

lgtm

[Jim Stichnoth, 2015-01-20 22:07:37]

PTAL.  For the first patchset, I didn't notice the new compiler warnings from
the fact that the GlobalContext* arg was unused.

[Karl, 2015-01-20 22:34:42]

lgtm

[Jim Stichnoth, 2015-01-20 22:54:02]

Committed patchset #2 (id:20001) manually as
a086b9135f3a492100ab349a5dccad8a1599f4bd (presubmit successful).