fix(VSnackbar): remove multi-line prop

[J-Sek]

Description

resolves #15996

Note: this PR should be followed by deprecating the field in 3.x

Markup:

<template>
  <div class="text-center">
    <v-btn color="red-darken-2" @click="snackbar = true"> Open Snackbar </v-btn>

    <v-snackbar v-model="snackbar" :timeout="-1" min-height="68">
      {{ text }}

      <template #actions>
        <v-btn color="red" variant="text" @click="snackbar = false">
          Close
        </v-btn>
      </template>
    </v-snackbar>
  </div>
</template>

<script setup>
  import { ref } from 'vue'

  const snackbar = ref(false)

  const text = `I am a multi-line snackbar. Confusing example. That's going away.`
</script>