syscall: remove stray TODO comment
syscall: remove stray TODO comment

This was addressed by CL 2816 and the same comment was deleted from
asm_linux_386.s.

Change-Id: Icc797993161d67e7c4f4cdb11c2b96ac88e00dd9
Reviewed-on: https://go-review.googlesource.com/c/go/+/261458
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>

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