[dev.link] cmd/internal/goobj2: move NoSplit to symbol flag

[dev.link] cmd/internal/goobj2: move NoSplit to symbol flag

Move NoSplit flag from FuncInfo to symbol flag, so this can be
accessed easily without reading the FuncInfo.

The CFunc flag is never used. Remove.

Change-Id: I8bf4fcb2f209434bb90ccc4987a4c3f28f003323
Reviewed-on: https://go-review.googlesource.com/c/go/+/220058
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>