Remove unnecessary theme attributes in AndroidManifest.xml (#496)

Author: SUPERCILEX

auth/src/main/AndroidManifest.xml

@@ -29,32 +29,27 @@
         <activity
             android:name=".ui.email.RecoverPasswordActivity"
             android:label="@string/title_recover_password_activity"
-            android:exported="false"
-            android:theme="@style/FirebaseUI"/>
+            android:exported="false"/>
 
         <activity
             android:name=".ui.email.RegisterEmailActivity"
             android:label="@string/sign_in_default"
-            android:exported="false"
-            android:theme="@style/FirebaseUI"/>
+            android:exported="false"/>
 
         <activity
             android:name=".ui.accountlink.WelcomeBackIdpPrompt"
             android:label="@string/title_welcome_back_idp_prompt"
-            android:exported="false"
-            android:theme="@style/FirebaseUI"/>
+            android:exported="false"/>
 
         <activity
             android:name=".ui.accountlink.WelcomeBackPasswordPrompt"
             android:label="@string/title_welcome_back_password_prompt"
-            android:exported="false"
-            android:theme="@style/FirebaseUI"/>
+            android:exported="false"/>
 
         <activity
             android:name=".ui.idp.AuthMethodPickerActivity"
             android:label="@string/default_toolbar_title"
-            android:exported="false"
-            android:theme="@style/FirebaseUI"/>
+            android:exported="false"/>
 
         <activity
             android:name="com.facebook.FacebookActivity"