Due to the many merges and changes to
37c3979e the default framebuffer
deletion "disappeared". Add it back to the destructor of Surface.

Update Surface_unittests and remove one of the two tests as they were
equivalent.

BUG=524495
BUG=angleproject:1137

Change-Id: I1309285ea00976ae2685628ea3f92731a9259718
Reviewed-on: https://chromium-review.googlesource.com/295153Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>