syscall: rm go:linkname from origRlimitNofile

Since CL 588076 runc can do fine without the kludge. The code accessing the symbol is now guarded with `go:build !go1.23` in all supported runc branches (main: [1], release-1.1: [2]).

This reverts part of CL 587219.

Updates #67401.

For #66797.

[1]: opencontainers/runc#4290
[2]: opencontainers/runc#4299

Change-Id: I204843a93c36857e21ab9b43bd7aaf046e8b9787
Reviewed-on: https://go-review.googlesource.com/c/go/+/587918
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: kolyshkin

src/syscall/rlimit.go

@@ -8,20 +8,9 @@ package syscall
 
 import (
 	"sync/atomic"
-	_ "unsafe"
 )
 
 // origRlimitNofile, if non-nil, is the original soft RLIMIT_NOFILE.
-//
-// origRlimitNofile should be an internal detail,
-// but widely used packages access it using linkname.
-// Notable members of the hall of shame include:
-//   - github.com/opencontainers/runc
-//
-// Do not remove or change the type signature.
-// See go.dev/issue/67401.
-//
-//go:linkname origRlimitNofile
 var origRlimitNofile atomic.Pointer[Rlimit]
 
 // Some systems set an artificially low soft limit on open file count, for compatibility