runtime: remove sys.HugePageSize

sys.HugePageSize was superceded in the last commit by physHugePageSize
which is determined dynamically by querying the operating system.

For #30333.

Change-Id: I827bfca8bdb347e989cead31564a8fffe56c66ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/173757


Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>