bugs:The code in function of get_all_requirements is duplicated

bugs:The code in function of get_all_requirements is duplicated

1、The virtualLink requirement of tosca.nodes.nfv.CP defined below:
In nodetype.py, the most code in functon of get_all_requirements is not
needed,becuase the property of requirements has realized the main logical
in current get_all_requirements. So the duplicated code will be deleted.

2、The bug will be submitted to openstack community.

JIRA: PARSER-37

Change-Id: I1a346ffc388546dd9c65a1b8d32e32859150d077
Signed-off-by: shangxdy <shang.xiaodong@zte.com.cn>