This commit enables vet/all for the js/wasm architecture. It got
skipped initially because the codebase did not fully compile yet
for js/wasm, which made vet/all fail.

startTimer and stopTimer are not needed in the syscall package.
Removed their assembly code since their Go stubs were already gone.

Change-Id: Icaeb6d903876e51ceb1edff7631f715a98c28696
Reviewed-on: https://go-review.googlesource.com/118657Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>