[dev.link] cmd/link: write data sections to heap in Asmb on Wasm

[dev.link] cmd/link: write data sections to heap in Asmb on Wasm

Make Wasm more like other architectures, writing data sections to
heap in Asmb instead of Asmb2. Then we can remove the
copy-on-write logic in applying relocations.

Change-Id: I26d5315ea9fba032fe4bdb9b5c7fe483611c4373
Reviewed-on: https://go-review.googlesource.com/c/go/+/230465
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>