Previously, isStaticCompositeLiteral would
return the wrong value for literals like:

[1]struct{ b []byte }{b: []byte{1}}

Note that the outermost component is an array,
but once we recurse into isStaticCompositeLiteral,
we never check again that arrays are actually arrays.

Instead of adding more logic to the guts of
isStaticCompositeLiteral, allow it to accept
any Node and return the correct answer.

Change-Id: I6af7814a9037bbc7043da9a96137fbee067bbe0e
Reviewed-on: https://go-review.googlesource.com/22247Reviewed-by: Keith Randall <khr@golang.org>