[dev.unified] cmd/compile: remove package height

[dev.unified] cmd/compile: remove package height

After CL 410654, symbols are now sorted by package path, package height
is not necessary anymore.

Updates #51734

Change-Id: I976edd2e574dda68eb5c76cf95645b9dce051393
Reviewed-on: https://go-review.googlesource.com/c/go/+/410342
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>