Revert "test: Increase RAM for TestKdumpNFS machine"

We have a better theory now of how kdump works and especially what
crashkernel means, and increasing the physical RAM of a machine is not
expected to help with growing initramfs sizes.

It _did_ help, for mysterious reasons, but not totally reliably. So
let's revert this, save some RAM, and wait for a real fix.

See https://bugzilla.redhat.com/show_bug.cgi?id=2305968

This reverts commit 3fb39bb.

test/verify/check-kdump

@@ -554,7 +554,7 @@ class TestKdumpNFS(KdumpHelpers):
 class TestKdumpNFSAnsible(KdumpHelpers):
  provision = {
  "cockpit": {"memory_mb": 512},
- "kdump_ansible_machine": {"address": "10.111.113.1/24", "memory_mb": 1500, "capture_console": True},
+ "kdump_ansible_machine": {"address": "10.111.113.1/24", "memory_mb": 1024, "capture_console": True},
  "nfs": {"image": TEST_OS_DEFAULT, "address": "10.111.113.2/24", "memory_mb": 512},
  }