Remove apache.aries.spifly and use the new equinox.spi in products

[HannesWell]

Use the new org.eclipse.equinox.spi framework extension, that implements the OSGi Service Loader Mediator specification and was introduced in

• Implement OSGi Service Loader Mediator Specification eclipse-equinox/equinox#295

The extension is already part of the o.e.equinox.core feature and doesn't need to be added explicitly.
Eventually it will not even be necessary to 'start/register' the extension in any way (i.e. adding it to the boot classpath via osgi.framework.extensions), once dynamic classloader-hook registration is supported:

• Support dynamic classloader-hook registration by framework extensions eclipse-equinox/equinox#1367

Using it allows to remove org.apache.aries.spifly.dynamic.bundle.

[iloveeclipse]

Looks like the sources are missing, we see test fail:
https://download.eclipse.org/eclipse/downloads/drops4/I20261008-2300/testresults/html/org.eclipse.releng.tests_ep442I-unit-linux-x86_64-java25_linux.gtk.x86_64_25.html

Plugin directory missing required files: /home/jenkins/agent/workspace/automated-tests/ep442I-unit-linux-x86_64-java25/workarea/I20261008-2300/eclipse-testing/test-eclipse/eclipse/plugins/org.eclipse.equinox.spi.source_1.0.0.v20261008-2211.jar;

java.lang.AssertionError: Plugin directory missing required files: /home/jenkins/agent/workspace/automated-tests/ep442I-unit-linux-x86_64-java25/workarea/I20261008-2300/eclipse-testing/test-eclipse/eclipse/plugins/org.eclipse.equinox.spi.source_1.0.0.v20261008-2211.jar;
at org.junit.Assert.fail(Assert.java:89)
at org.junit.Assert.assertTrue(Assert.java:42)
at org.eclipse.releng.tests.BuildTests.testPluginFiles(BuildTests.java:182)
at java.base/java.lang.reflect.Method.invoke(Method.java:565)