package/nfs-utils: nfsiostat uses python3, not python2

nfsiostat is a python3 script, so keep it if python3 is enabled and not
python2:

head -n 1 target/usr/sbin/nfsiostat
 #!/usr/bin/python3

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/nfs-utils/nfs-utils.mk

@@ -114,7 +114,7 @@ define NFS_UTILS_REMOVE_NFSIOSTAT
 endef
 
 # nfsiostat is interpreted python, so remove it unless it's in the target
-NFS_UTILS_POST_INSTALL_TARGET_HOOKS += $(if $(BR2_PACKAGE_PYTHON),,NFS_UTILS_REMOVE_NFSIOSTAT)
+NFS_UTILS_POST_INSTALL_TARGET_HOOKS += $(if $(BR2_PACKAGE_PYTHON3),,NFS_UTILS_REMOVE_NFSIOSTAT)
 
 define HOST_NFS_UTILS_BUILD_CMDS
 	$(MAKE) -C $(@D)/tools/rpcgen