For #19797 - Remove FenixAccountManager#signedInToFxa

After the changes from this patch this api is not used anymore so to prevent
future misuses of it this is removed in favor of the new "accountState".

app/src/main/java/org/mozilla/fenix/components/accounts/FenixAccountManager.kt

@@ -34,16 +34,6 @@ open class FenixAccountManager(context: Context) {
                 AccountState.AUTHENTICATED
             }
         }
-
-    /**
-     * Check if the current account is signed in and authenticated.
-     */
-    fun signedInToFxa(): Boolean {
-        val account = accountManager.authenticatedAccount()
-        val needsReauth = accountManager.accountNeedsReauth()
-
-        return account != null && !needsReauth
-    }
 }
 
 /**

app/src/test/java/org/mozilla/fenix/components/accounts/FenixAccountManagerTest.kt

@@ -11,9 +11,7 @@ import mozilla.components.concept.sync.OAuthAccount
 import mozilla.components.concept.sync.Profile
 import mozilla.components.service.fxa.manager.FxaAccountManager
 import org.junit.Assert.assertEquals
-import org.junit.Assert.assertFalse
 import org.junit.Assert.assertSame
-import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -64,42 +62,6 @@ class FenixAccountManagerTest {
         assertEquals(null, result)
     }
 
-    @Test
-    fun `GIVEN an account is signed in and authenticated THEN check returns true`() {
-        every { accountManagerComponent.authenticatedAccount() } returns account
-        every { accountManagerComponent.accountNeedsReauth() } returns false
-        every { context.components.backgroundServices.accountManager } returns accountManagerComponent
-
-        fenixFxaManager = FenixAccountManager(context)
-
-        val signedIn = fenixFxaManager.signedInToFxa()
-        assertTrue(signedIn)
-    }
-
-    @Test
-    fun `GIVEN an account is signed in and NOT authenticated THEN check returns false`() {
-        every { accountManagerComponent.authenticatedAccount() } returns account
-        every { accountManagerComponent.accountNeedsReauth() } returns true
-        every { context.components.backgroundServices.accountManager } returns accountManagerComponent
-
-        fenixFxaManager = FenixAccountManager(context)
-
-        val signedIn = fenixFxaManager.signedInToFxa()
-        assertFalse(signedIn)
-    }
-
-    @Test
-    fun `GIVEN an account is not signed in THEN check returns false`() {
-        every { accountManagerComponent.authenticatedAccount() } returns null
-        every { accountManagerComponent.accountNeedsReauth() } returns true
-        every { context.components.backgroundServices.accountManager } returns accountManagerComponent
-
-        fenixFxaManager = FenixAccountManager(context)
-
-        val signedIn = fenixFxaManager.signedInToFxa()
-        assertFalse(signedIn)
-    }
-
     @Test
     fun `GIVEN no account exists WHEN accountState is called THEN it returns AccountState#NO_ACCOUNT`() {
         every { context.components.backgroundServices.accountManager } returns accountManagerComponent