debug/elf: map/slice literals janitoring

Simplify slice/map literal expressions.
Caught with gofmt -d -s, fixed with gofmt -w -s
Reformatted some expressions to improve readability.

Change-Id: Iaf123e6bd49162ec45c59297ad3b002ca59443bc
Reviewed-on: https://go-review.googlesource.com/13850Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>