Revert "runtime: move epoll syscalls to runtime/internal/syscall"

Revert "runtime: move epoll syscalls to runtime/internal/syscall"

This reverts CL 421994.

Reason for revert: breaks runtime.TestCheckPtr2

For #53824
For #51087

Change-Id: I044ea4d6efdffe0a4b7fb0d2bb3717d9f391fc59
Reviewed-on: https://go-review.googlesource.com/c/go/+/437295
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>