There were 10 implementations of the trivial bool2int function, 9 of which
were the only thing in their file.  Remove all of them in favor of one in
cmd/internal/obj.

Change-Id: I9c51d30716239df51186860b9842a5e9b27264d3
Reviewed-on: https://go-review.googlesource.com/9230Reviewed-by: Ian Lance Taylor <iant@golang.org>