[dev.link] cmd/link: clean up some pclntab state
[dev.link] cmd/link: clean up some pclntab state

Clean up some pclntab state, specifically:
1) Remove the oldPclnState type.
2) Move a structure out of pclnState, that was holding some memory.
3) Stop passing container around everywhere and calling emitPcln. Use a
   slice of function symbols instead.

Change-Id: I74e916564cd769a706750d024e55ee0d811a79da
Reviewed-on: https://go-review.googlesource.com/c/go/+/248379
Run-TryBot: Jeremy Faller <b3f594e10a9edcf5413cf1190121d45078c62290@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

cloudflare/go,cloudflare/go,nawawi/go,nawawi/go,cloudflare/go,CAFxX/go,CAFxX/go,golang/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,golang/go,cloudflare/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,CAFxX/go,CAFxX/go