HostStubGen: Fix direct outer class detection

If there's a nested class like A$B$C and C doesn't have a class-wide
policy, HSG was supposed to look at A$B's ("direct outer class") policy,
but it was using A's policy. Fixed it.

Bug: 311174191
Test: ./scripts/run-all-tests.sh
Test: atest --host CtsGraphicsTestCasesRavenwood \
    CtsTextTestCasesRavenwood \
    CtsOsTestCasesRavenwood \
    CtsAccountManagerTestCasesRavenwood \
    CtsContentTestCasesRavenwood \
    CtsProtoTestCasesRavenwood \
    CtsUtilTestCasesRavenwood \
    CtsDatabaseTestCasesRavenwood
Change-Id: I4881caac5e91366cf60e1aa232ecaf6b7c88aecf