Tab swiping: Clean up unused fixes behind feature flags (#6025)

Task/Issue URL:
https://app.asana.com/1/137249556945/project/72649045549333/task/1210187246401089?focus=true

### Description

This PR removes unused fixes and the associated feature flags.


---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
  - https://app.asana.com/0/0/1208271988740971

Author: 0nko

app/src/main/java/com/duckduckgo/app/browser/tabs/adapter/FragmentStateAdapter.java

@@ -210,11 +210,7 @@ public void onDetachedFromRecyclerView(@NonNull RecyclerView recyclerView) {
     @NonNull
     @Override
     public final FragmentViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
-        if (mSwipingTabsFeature != null && mSwipingTabsFeature.isTabSwipingFix1Enabled()) {
-            return FragmentContainerViewHolder.create(parent);
-        } else {
-            return FrameLayoutViewHolder.create(parent);
-        }
+        return FrameLayoutViewHolder.create(parent);
     }
 
     @Override
@@ -470,13 +466,7 @@ void addViewToContainer(@NonNull View v, @NonNull FrameLayout container) {
     }
 
     private void throwDesignAssumptionViolatedException() {
-        throw new IllegalStateException(
-            String.format(
-                "Design assumption violated: Fix1 enabled: %s, Fix2 enabled: %s",
-                mSwipingTabsFeature.isTabSwipingFix1Enabled(),
-                mSwipingTabsFeature.isTabSwipingFix2Enabled()
-            )
-        );
+        throw new IllegalStateException("Design assumption violated");
     }
 
     @Override
@@ -562,11 +552,6 @@ private void removeFragment(long itemId) {
     }
 
     private void hideFragment(long itemId) {
-        // do not attempt to hide fragments if the ViewPager is in a transient state
-        if (shouldDelayFragmentTransactions() && mSwipingTabsFeature.isTabSwipingFix2Enabled()) {
-            return;
-        }
-
         Fragment fragment = mFragments.get(itemId);
 
         if (fragment == null) {

app/src/main/java/com/duckduckgo/app/browser/tabs/adapter/FragmentViewHolder.kt

@@ -18,7 +18,6 @@ package com.duckduckgo.app.browser.tabs.adapter
 import android.view.View
 import android.view.ViewGroup
 import android.widget.FrameLayout
-import androidx.fragment.app.FragmentContainerView
 import androidx.recyclerview.widget.RecyclerView
 
 /**
@@ -46,19 +45,3 @@ class FrameLayoutViewHolder private constructor(container: FrameLayout) : Fragme
         }
     }
 }
-
-class FragmentContainerViewHolder private constructor(container: FragmentContainerView) : FragmentViewHolder(container) {
-    companion object {
-        @JvmStatic
-        fun create(parent: ViewGroup): FragmentViewHolder {
-            val container = FragmentContainerView(parent.context)
-            container.layoutParams = ViewGroup.LayoutParams(
-                ViewGroup.LayoutParams.MATCH_PARENT,
-                ViewGroup.LayoutParams.MATCH_PARENT,
-            )
-            container.id = View.generateViewId()
-            container.isSaveEnabled = false
-            return FragmentContainerViewHolder(container)
-        }
-    }
-}

common/common-ui/src/main/java/com/duckduckgo/common/ui/tabs/SwipingTabsFeature.kt

@@ -28,20 +28,11 @@ import com.duckduckgo.feature.toggles.api.Toggle.InternalAlwaysEnabled
 )
 interface SwipingTabsFeature {
     // The main kill switch for the feature
-    @Toggle.DefaultValue(DefaultFeatureValue.FALSE)
-    @InternalAlwaysEnabled
+    @Toggle.DefaultValue(DefaultFeatureValue.INTERNAL)
     fun self(): Toggle
 
     // The toggle used for staged rollout to external users
     @Toggle.DefaultValue(DefaultFeatureValue.FALSE)
     @InternalAlwaysEnabled
     fun enabledForUsers(): Toggle
-
-    // The toggle used to enable a potential fix for https://app.asana.com/0/1207418217763355/1209914129786590/f
-    @Toggle.DefaultValue(DefaultFeatureValue.FALSE)
-    fun tabSwipingFix1(): Toggle
-
-    // The toggle used to enable a potential fix for https://app.asana.com/0/1207418217763355/1209914129786590/f
-    @Toggle.DefaultValue(DefaultFeatureValue.FALSE)
-    fun tabSwipingFix2(): Toggle
 }

common/common-ui/src/main/java/com/duckduckgo/common/ui/tabs/SwipingTabsFeatureProvider.kt

@@ -27,12 +27,4 @@ class SwipingTabsFeatureProvider @Inject constructor(
     val isEnabled: Boolean by lazy {
         swipingTabsFeature.self().isEnabled() && swipingTabsFeature.enabledForUsers().isEnabled()
     }
-
-    val isTabSwipingFix1Enabled by lazy {
-        swipingTabsFeature.tabSwipingFix1().isEnabled()
-    }
-
-    val isTabSwipingFix2Enabled by lazy {
-        swipingTabsFeature.tabSwipingFix2().isEnabled()
-    }
 }