syscall: remove //sysnb comment generating Setreuid for linux/arm64
syscall: remove //sysnb comment generating Setreuid for linux/arm64

CL 210639 moved the //sysnb for Setreuid from syscall_linux_$GOARCH.go
to syscall_linux.go but forgot to remove the comment from
syscall_linux_arm64.go which leads to Setreuid being generated twice for
linux/arm64. Remove that //sysnb comment to avoid this.

Change-Id: I2c8ad95f786530ca964685b0a4fe463c64764307
Reviewed-on: https://go-review.googlesource.com/c/go/+/350531
Trust: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

nawawi/go,golang/go,cloudflare/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go,golang/go,nawawi/go,CAFxX/go,nawawi/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,CAFxX/go,golang/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,cloudflare/go,golang/go