cmd/internal/goobj: remove Pcdata from object file

cmd/internal/goobj: remove Pcdata from object file

As of CL 247399 we use separate symbols for PCDATA. There is no
more need for writing PCDATA directly into the object file as a
separate block.

Change-Id: I942d1a372540415e0cc07fb2a01f79718a264142
Reviewed-on: https://go-review.googlesource.com/c/go/+/352610
Trust: Cherry Mui <cherryyz@google.com>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>