Remove feedback preferences and update layouts

This commit removes the feedback preference screen and its associated resources:
- `ic_notification_update.xml`
- `preferences_feedback.xml`
- `key_feedback` string resource

Additionally, it removes `android:layout_marginTop="0dp"` from the `lesson_section_header` include in the following layout files:
- `activity_buttons.xml`
- `activity_spinner.xml`
- `activity_image_buttons.xml`
- `activity_clock.xml`
- `activity_progress_bar.xml`
- `activity_chronometer.xml`
- `activity_linear_layout.xml`
- `activity_switch.xml`

Author: MihaiCristianCondrea

app/src/main/res/drawable-anydpi/ic_notification_update.xml

@@ -25,7 +25,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <com.google.android.material.textview.MaterialTextView

app/src/main/res/layout/activity_buttons.xml

@@ -26,7 +26,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <Chronometer

app/src/main/res/layout/activity_chronometer.xml

@@ -26,7 +26,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <com.google.android.material.textview.MaterialTextView

app/src/main/res/layout/activity_clock.xml

@@ -25,7 +25,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <androidx.appcompat.widget.AppCompatImageButton

app/src/main/res/layout/activity_image_buttons.xml

@@ -25,7 +25,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <com.google.android.material.textview.MaterialTextView

app/src/main/res/layout/activity_linear_layout.xml

@@ -25,7 +25,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <com.google.android.material.textview.MaterialTextView

app/src/main/res/layout/activity_progress_bar.xml

@@ -25,7 +25,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <com.google.android.material.textview.MaterialTextView

app/src/main/res/layout/activity_spinner.xml

@@ -27,7 +27,6 @@
             <include
                 android:id="@+id/layout_preview_header"
                 layout="@layout/lesson_section_header"
-                android:layout_marginTop="0dp"
                 tools:text="@string/layout_preview" />
 
             <com.google.android.material.textview.MaterialTextView

app/src/main/res/layout/activity_switch.xml

@@ -15,7 +15,6 @@
     <string name="key_firebase_performance" translatable="false">firebase_performance</string>
     <string name="key_device_info" translatable="false">device_info</string>
     <string name="key_open_source_licenses" translatable="false">open_source_licenses</string>
-    <string name="key_feedback" translatable="false">feedback</string>
     <string name="key_consent_analytics" translatable="false">consent_analytics_storage</string>
     <string name="key_consent_ad_storage" translatable="false">consent_ad_storage</string>
     <string name="key_consent_ad_user_data" translatable="false">consent_ad_user_data</string>