Remove CNI backend configuration from runtime

Remove runtime configuration options for CNI network backend:

Runtime options:
- Remove WithNetworkBackend() runtime option function
- Function allowed setting network backend programmatically

Flag handling:
- Remove --network-backend flag change detection
- Remove call to WithNetworkBackend() when flag changed
- Remove TODO comment about CNI plugins directory flag

The network backend configuration is now handled entirely by the
vendored common/libnetwork code, which will default to Netavark.
There is no longer any way to configure CNI as the network backend
through Podman's runtime initialization.

Note: libpod/info.go keeps existing NetworkBackend reporting logic
which will automatically report "netavark" as the only backend since
configuration defaults to netavark and cannot be changed to CNI.

Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>

pkg/domain/infra/runtime_libpod.go

@@ -164,9 +164,6 @@ func getRuntime(ctx context.Context, fs *flag.FlagSet, opts *engineOpts) (*libpo
 	if fs.Changed("tmpdir") {
 		options = append(options, libpod.WithTmpDir(cfg.ContainersConf.Engine.TmpDir))
 	}
-	if fs.Changed("network-backend") {
-		options = append(options, libpod.WithNetworkBackend(cfg.ContainersConf.Network.NetworkBackend))
-	}
 
 	if fs.Changed("events-backend") {
 		options = append(options, libpod.WithEventsLogger(cfg.ContainersConf.Engine.EventsLogger))
@@ -208,8 +205,6 @@ func getRuntime(ctx context.Context, fs *flag.FlagSet, opts *engineOpts) (*libpo
 		options = append(options, libpod.WithStaticDir(opts.config.ContainersConfDefaultsRO.Engine.StaticDir))
 	}
 
-	// TODO flag to set CNI plugins dir?
-
 	if !opts.withFDS {
 		options = append(options, libpod.WithEnableSDNotify())
 	}