Removed wifi feature check from teardown in WifiMigrationTest

WifiMigrationTest class has wifi feature check condition in both
setup and teardown. So when wifi feature is disabled, setup function
asserts for test exit and teardown function also asserts which makes
testcase to crash because of multiple asserts

Bug: 436483108
Flag: EXEMPT test change
Test: CtsWifiNonUpdatableTestCases
Change-Id: I2cb2a78758fb3bf072ed0d4a197dceacfdb0e095