Removing "Server" response header

[#1]

I'm trying to remove the "Server" : "Apigee Router" header from the response.

I tried removing it using an Assign Message Policy in the Proxy Endpoints' PreFlow but it didn't do it.

Then tried the same in PostFlow and then in TargetEndPoints' pre/post flow - still didn't work.

Here's the policy I have in place:

<AssignMessage async="false" continueOnError="false" enabled="true" name="removeServerHeader">
    <DisplayName>removeServerHeader</DisplayName>
    <AssignTo createNew="false" transport="http" type="response"/>
    <Properties/>
    <Remove>
        <Headers>
            <Header name="Server"/>
        </Headers>
    </Remove>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</AssignMessage>