Remove unused method from MatchAllNetworkSpecifier

checkNotMatchAllNetworkSpecifier is a hidden method inside
MatchAllNetworkSpecifier, and the callers have implemented
the logic by themselves to prevent calling hidden method.
Remove it because there is no one using it.

Bug: 172183305
Test: atest FrameworksNetTests
Change-Id: I22a3a99f2b4ec6f4b57ef8867b72d48db2f0c1f6