Remove ~half the tests in StatementSwitchToExpressionSwitchTest.

There's not a lot of value add in asserting that a finding was found _and_ the refactoring. The existence of a refactoring implies that a fix was emitted, so all that's being asserted is the location.. which isn't super interesting to repeat each time, given it's always the switch.

PiperOrigin-RevId: 748301161

Author: graememorgan