Use o.e.platform.ide when building the platform-source zip

... to replace the removed org.eclipse.platform.sdk

Additionally remove the unused
org.eclipse.platform.releng.tychoeclipsebuilder/rcp/pom.xml. From the
history it looks like it was introduced as pom fro the also removed
rcp.product.

Follow-up on
eclipse-platform#1235

eclipse.platform.releng.tychoeclipsebuilder/repos/platformrepo.xml

@@ -41,7 +41,7 @@
       <iu id="org.eclipse.equinox.p2.user.ui.source.feature.group" version="" />
       <iu id="org.eclipse.rcp.configuration.feature.group" version="" />
       <iu id="org.eclipse.equinox.executable.feature.group" version="" />
-      <iu id="org.eclipse.platform.sdk" version="" />
+      <iu id="org.eclipse.platform.ide" version="" />
       <slicingOptions includeOptional="false" includeNonGreedy="false" />
     </p2.mirror>
         <p2.remove.iu>