set enablePlatformCertificateValidation to false on iOS by default (#2663)
set enablePlatformCertificateValidation to false on iOS by default (#2663)

Signed-off-by: 45e8a3487ba367cdc396d74d8966a3eb7c97c70d@google.com

Was set to true inadvertently in #2638.
envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile