It should not be possible to redeclare arrays. This seems to be another
thing left over from earlier erroneous code which allowed declaring
unsized arrays.

TEST=angle_unittests
BUG=angleproject:941

Change-Id: I711565230b35df077f268cec6fdeac6c4c03b4cd
Reviewed-on: https://chromium-review.googlesource.com/264672Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>