qemu: Remove pmu limitation in nested virtualization of amd/ppc64le

[ port from runtime commit 18662e16687453185ff4cf99b495a34e3ea9935f ]

It's up to the user enable/disable pmu. After previous commit, the default
pmu option has been set to off.

This patch removes the hard limitation and unit test codes.

Signed-off-by: Jia He <justin.he@arm.com>
Signed-off-by: Peng Tao <bergwolf@hyper.sh>

src/runtime/virtcontainers/qemu_amd64.go

@@ -158,9 +158,6 @@ func (q *qemuAmd64) bridges(number uint32) {
 
 func (q *qemuAmd64) cpuModel() string {
 	cpuModel := defaultCPUModel
-	if q.nestedRun {
-		cpuModel += ",pmu=off"
-	}
 
 	// VMX is not migratable yet.
 	// issue: https://github.com/kata-containers/kata-containers/src/runtime/issues/1750

src/runtime/virtcontainers/qemu_amd64_test.go

@@ -95,11 +95,6 @@ func TestQemuAmd64CPUModel(t *testing.T) {
 	model := amd64.cpuModel()
 	assert.Equal(expectedOut, model)
 
-	amd64.enableNestingChecks()
-	expectedOut = defaultCPUModel + ",pmu=off"
-	model = amd64.cpuModel()
-	assert.Equal(expectedOut, model)
-
 	amd64.disableNestingChecks()
 	base, ok := amd64.(*qemuAmd64)
 	assert.True(ok)