refactor(shell): delete EmptyTabScreen

Its own KDoc said M5 to M8 would replace it. M8 was the last one: every tab
now has content of its own, so the placeholder has no caller left.

app/src/main/java/de/jeanlucmakiola/clockula/ui/shell/ShellDefaults.kt

@@ -1,20 +1,9 @@
 package de.jeanlucmakiola.clockula.ui.shell
 
-import androidx.compose.foundation.layout.Spacer
-import androidx.compose.foundation.layout.height
-import androidx.compose.foundation.layout.padding
-import androidx.compose.material3.MaterialTheme
-import androidx.compose.material3.Text
-import androidx.compose.runtime.Composable
 import androidx.compose.runtime.ProvidableCompositionLocal
 import androidx.compose.runtime.compositionLocalOf
-import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
-import de.jeanlucmakiola.floret.components.CollapsingScaffold
-import de.jeanlucmakiola.floret.components.GroupedListInset
-import de.jeanlucmakiola.floret.components.GroupedSurface
-import de.jeanlucmakiola.floret.components.Position
 import kotlin.time.Duration
 import kotlin.time.Duration.Companion.seconds
 
@@ -43,34 +32,3 @@ object ShellDefaults {
  * pill comes and goes, and a static local would recompose the whole subtree.
  */
 val LocalLivePillInset: ProvidableCompositionLocal<Dp> = compositionLocalOf { 0.dp }
-
-/**
- * A top-level tab's title bar over a single sentence on a grouped surface —
- * the shape M4's four tabs share while their content belongs to M5–M8. Each
- * tab keeps the pill's band clear through [LocalLivePillInset], so a countdown
- * never sits on top of the last row.
- *
- * Lives here rather than being written out four times: the tabs differ only in
- * two strings today, and each of M5–M8 replaces its own tab outright.
- */
-@Composable
-internal fun EmptyTabScreen(
-    title: String,
-    message: String,
-    modifier: Modifier = Modifier,
-) {
-    CollapsingScaffold(title = title, modifier = modifier) {
-        GroupedSurface(
-            position = Position.Alone,
-            modifier = Modifier.padding(horizontal = GroupedListInset),
-        ) {
-            Text(
-                text = message,
-                style = MaterialTheme.typography.bodyLarge,
-                color = MaterialTheme.colorScheme.onSurfaceVariant,
-                modifier = Modifier.padding(horizontal = 20.dp, vertical = 24.dp),
-            )
-        }
-        Spacer(Modifier.height(LocalLivePillInset.current))
-    }
-}