doc/go1.18: don't mention -buildinfo flag
doc/go1.18: don't mention -buildinfo flag

It was removed in CL 378576.

For #50501

Change-Id: I26b8f0e99a40fa5c616aa4849a6ab15dd0d072f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/379314
Trust: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

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