cmd/compile: remove asmtest infrastructure
cmd/compile: remove asmtest infrastructure

Not used anymore, all tests have been migrated to
the top-level testsuite.

Change-Id: I536e6c14f62153c01e4966ad41e1501b38494c7f
Reviewed-on: https://go-review.googlesource.com/107336
Run-TryBot: Giovanni Bajo <387225cd66f97dc812a00599dbc5b6544a73295c@develer.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,cloudflare/go,akutz/go,akutz/go,golang/go,golang/go,golang/go,nawawi/go,cloudflare/go,josharian/go,akutz/go,josharian/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go,josharian/go,golang/go,josharian/go,cloudflare/go,akutz/go,cloudflare/go,nawawi/go,CAFxX/go,cloudflare/go,akutz/go,josharian/go,golang/go,cloudflare/go,nawawi/go,josharian/go,CAFxX/go,nawawi/go,akutz/go,CAFxX/go,nawawi/go,CAFxX/go,nawawi/go,akutz/go,josharian/go,josharian/go,akutz/go