CI: Remove L2sim proxy build support

Remove the `BuildProxy` method, `Build_Proxy` action, `proxyCommit`
attribute, and all associated XML configuration and unit tests.

The oai-lte-5g-multi-ue-proxy repository has not received any updates
in over two years, and the proxy commit currently used for the build
is outdated as well. Although the proxy image is still required by
RAN-L2-Sim-Test-4G and must remain available on the test machine,
building it as part of the CI pipeline is dropped in this commit.

Instead, the CI will now assume that the corresponding proxy image is
already present as an external dependency, similarly to how CN images
are handled.

Signed-off-by: Jaroslava Fiedlerova <jaroslava.fiedlerova@openairinterface.org>

ci-scripts/tests/build.py

@@ -33,10 +33,5 @@ class TestBuild(unittest.TestCase):
 			cmd.run(f"rm -rf {self._d}")
 			cmd.run(f'rm -rf {self.ctx.logPath}')
 
-	def test_build_proxy(self):
-		self.cont.proxyCommit = "b64d9bce986b38ca59e8582864ade3fcdd05c0dc"
-		success = self.cont.BuildProxy(self.ctx, self.node, self.html)
-		self.assertTrue(success)
-
 if __name__ == '__main__':
 	unittest.main()