ec2_instance - fix instance creation with IPv6 (#40334)

IPv6 addresses and IPv6 address count may not be specified on the same request https://docs.aws.amazon.com/cli/latest/reference/ec2/assign-ipv6-addresses.html#options

lib/ansible/modules/cloud/amazon/ec2_instance.py

@@ -869,7 +869,6 @@ def build_network_spec(params, ec2=None):
 
         if interface_params.get('ipv6_addresses'):
             spec['Ipv6Addresses'] = [{'Ipv6Address': a} for a in interface_params.get('ipv6_addresses', [])]
-            spec['Ipv6AddressCount'] = len(spec['Ipv6Addresses'])
 
         if interface_params.get('private_ip_address'):
             spec['PrivateIpAddress'] = interface_params.get('private_ip_address')