[HostStubGen] Fix class-wide policy filter

- It didn't handle class names with '$' properly
- It uses unnecessary loops, as recursion already handles it

Bug: 292141694
Flag: EXEMPT host test change only
Test: atest hoststubgen-test-tiny-test
Test: $ANDROID_BUILD_TOP/frameworks/base/ravenwood/scripts/run-ravenwood-tests.sh
Change-Id: I8e2cfebfd115a9e450dce3e4aecd6b53e0ad46f2