e2e: node: memory manager: build everywhere, run only on linux

Since the KEP 4885
(https://github.com/kubernetes/enhancements/blob/master/keps/sig-windows/4885-windows-cpu-and-memory-affinity/README.md)
memory manager is supported also on windows.

Plus, we want to add podresources e2e tests which configure
the memory manager. Both these facts suggest it's useful to build
the e2e memory manager tests on all OSes, not just on linux;

However, since we are not sure we are ready to run these tests
everywhere, we tag them LinuxOnly to keep preserve most of the
old behavior.

Signed-off-by: Francesco Romani <fromani@redhat.com>

test/e2e_node/memory_manager_test.go

@@ -1,6 +1,3 @@
-//go:build linux
-// +build linux
-
 /*
 Copyright 2017 The Kubernetes Authors.
 
@@ -242,7 +239,7 @@ func getAllNUMANodes() []int {
 }
 
 // Serial because the test updates kubelet configuration.
-var _ = SIGDescribe("Memory Manager", framework.WithDisruptive(), framework.WithSerial(), feature.MemoryManager, func() {
+var _ = SIGDescribe("Memory Manager", "[LinuxOnly]", framework.WithDisruptive(), framework.WithSerial(), feature.MemoryManager, func() {
 	// TODO: add more complex tests that will include interaction between CPUManager, MemoryManager and TopologyManager
 	var (
 		allNUMANodes             []int