Don't check selectedRoutes of created sesions

There are cases that a newly create session does not contain
the requested route. (e.g. static group)
This CL removes check that disallowed those cases.

Bug: 159881597
Test: Run CTS, atest mediaroutertest and manually
using support v7 demos, which is edited to call
notifySessionCreated with member routes selected

Change-Id: I30741d2f3587d0fa9ee5a10fdb8fab9e0d82c721