It is good that we know that we can execute any api object method from WS, so you still can delete your role relationship:
1. First you need to get persistent id of your relationship
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://www.ca.com/UnicenterServicePlus/ServiceDesk">
<soapenv:Header/>
<soapenv:Body>
<ser:getLrelValues>
<sid>1347379007</sid>
<contextObject>cnt:2205ACC2A7449B43A179DA002501123B</contextObject>
<lrelName>roles</lrelName>
<startIndex>0</startIndex>
<endIndex>3</endIndex>
<attributes>
<!--1 or more repetitions:-->
<string>role_obj</string>
</attributes>
</ser:getLrelValues>
</soapenv:Body>
</soapenv:Envelope>
you will receive response similar to this:
<UDSObject>
<Handle>cnt_role:400053</Handle>
<Attributes>
<Attribute DataType="2005">
<AttrName>role_obj</AttrName>
<AttrValue>10024</AttrValue>
</Attribute>
</Attributes>
</UDSObject>
<UDSObject>
<Handle>cnt_role:400052</Handle>
Ok lets try to remove cnt_role:400053 relation, we will be using SOAP METHOD callServerMethod to call delete_wc spel method that is defined on api object. We will need to pass null value to the method so we need to include one more namespace xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://www.ca.com/UnicenterServicePlus/ServiceDesk" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Header/>
<soapenv:Body>
<ser:callServerMethod>
<sid>1347379007</sid>
<methodName>delete_wc</methodName>
<factoryName>api</factoryName>
<formatList></formatList>
<parameters>
<!--1 or more repetitions:-->
<string>cnt_role</string>
<string>id = 400053</string>
<string xsi:nil='true' />
</parameters>
</ser:callServerMethod>
</soapenv:Body>
</soapenv:Envelope>
Now you can use getLrelValues method to check that relation is removed