qemu: do not define known no-op features

qemu: do not define known no-op features

Qemu dropped cpu features for osxsave and ospke [1][2].
The reason for the instant removal is that those features were never
configurable as discussed in [3].

Fortunately the use cases adding those flags in the past are rare, but
they exist. One that I identified are e.g. older virt-install when used
with --cpu=host-model and there always could be the case of a user
adding it to the guest xml.

This triggers an issue like:
  qemu-system-x86_64: can't apply global Broadwell-noTSX-x86_64-
  cpu.osxsave=on: Property '.osxsave' not found

Ensure that this does no more break spawning newer qemu versions by
not rendering those features into the qemu command line.

Fixes: https://bugs.launchpad.net/fedora/+source/qemu/+bug/1825195
Resolves: https://bugzilla.redhat.com/1644848

[1]: https://git.qemu.org/?p=qemu.git;a=commit;h=f1a2352
[2]: https://git.qemu.org/?p=qemu.git;a=commit;h=9ccb978
[3]: https://www.mail-archive.com/qemu-devel@nongnu.org/msg561877.html

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>