refactor(magnification suw): hide follow typing toggle in setup wizard

Originally we cache mFollowingTypingSwitchPreference in fragment so in
ToggleScreenMagnificationPreferenceFragmentForSetupWizard we can set the
preference visible to false to hide it. After creating MagnificationFeaturePreferenceController,
the MagnificationFollowTypingPreferenceController can extend it and
check isInSetupWizard internally then dicide whether to hide. Therefore,
we don't need to cache mFollowingTypingSwitchPreference in fragment
and let the fragment control the preference visibility anymore.

Bug: 340721852
Flag: NONE
Test: manually
      atest MagnificationFollowTypingPreferenceControllerTest
      atest ToggleScreenMagnificationPreferenceFragmentForSetupWizardTest
      atest ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: I44f7f0589b2df3d83a27139323fc68a0561f1cfa