Fix missing controller key and remove onCreatePreferences

1) A missing controller key for CellularSecurityEncryptionDividerController
was causing the corresponding UI element's getAvailabilityStatus to not
be called. 2) The inclusion of onCreatePreferences in
CellularSecuritySettingsFragment was causing other UI element's
controllers to not be called correctly.

Bug: b/373942609
Test: atest CellularSecurityPreferenceControllerTest
Test: atest CellularSecurityEncryptionDividerControllerTest
Flag: EXEMPT bugfix
Change-Id: Ic01a609311d7bd84ee835ffbede793fe2d7756ae