multiplatform: remove unused clipboard state polling that froze desktop UI (#7237)

The desktop app polled full clipboard contents every second on the AWT
event thread to update ChatModel.clipboardHasText. On X11, each read
blocks up to sun.awt.datatransfer.timeout (10s) when the selection owner
does not respond (e.g. after KeePassXC's clipboard auto-clear), making
every click/scroll wait ~9s. clipboardHasText has had no readers since
its only consumer was removed in #4398, so the whole mechanism (desktop
poll, Android clip listener, onResume refresh, expect/actual, state
field) is deleted. See plans/2026-07-11-fix-desktop-clipboard-freeze.md.

apps/multiplatform/common/src/androidMain/kotlin/chat/simplex/common/views/helpers/Utils.android.kt

@@ -1,7 +1,5 @@
 package chat.simplex.common.views.helpers
 
-import android.content.ClipboardManager
-import android.content.Context
 import android.content.res.Resources
 import android.graphics.*
 import android.graphics.Typeface
@@ -14,7 +12,6 @@ import android.text.SpannedString
 import android.text.style.*
 import android.util.Base64
 import android.view.WindowManager
-import androidx.compose.runtime.*
 import androidx.compose.ui.graphics.*
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.*
@@ -58,19 +55,6 @@ fun keepScreenOn(on: Boolean) {
   }
 }
 
-@Composable
-actual fun SetupClipboardListener() {
-  DisposableEffect(Unit) {
-    val service = androidAppContext.getSystemService(Context.CLIPBOARD_SERVICE) as ClipboardManager
-    val listener = { chatModel.clipboardHasText.value = service.hasPrimaryClip() }
-    chatModel.clipboardHasText.value = service.hasPrimaryClip()
-    service.addPrimaryClipChangedListener(listener)
-    onDispose {
-      service.removePrimaryClipChangedListener(listener)
-    }
-  }
-}
-
 actual fun escapedHtmlToAnnotatedString(text: String, density: Density): AnnotatedString {
   return spannableStringToAnnotatedString(HtmlCompat.fromHtml(text, HtmlCompat.FROM_HTML_MODE_LEGACY), density)
 }