internal/trace: clean up parser.go

internal/trace: clean up parser.go

parser.go is an old file that contains trace v1 definitions and a second
equivalent definition for stack frames. These are redundant and useless.
Delete these definitions and rename the file to fakep.go, which
describes the only thing left in this file, a bunch of fake P IDs used
by the trace viewer.

We should consider moving the fake P definitions elsewhere, too.

Change-Id: Ifd0768bd73c39009069445afe0155f1e352f00c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/644875
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>