docs: Document removal of 64-bit on 32-bit emulation

With acce728cbc6c we disallowed configuring 64-bit guests on
32-bit hosts, but forgot to document that in removed-features.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
1 file changed