fix(VAutocomplete/VCombobox): allow delete in single selection mode

[yuwu9145]

fixes #19369

In multiple selection mode, Backspace key selects the last item first then remove on second Backspace event.

In single selection mode, remove selected item directly on first Backspace event.

Description

Markup:

<template>
  <v-autocomplete
    label="Autocomplete"
    chips
    :items="['California', 'Colorado', 'Florida', 'Georgia', 'Texas', 'Wyoming']"
  />
  <v-combobox
    chips
    label="Combobox"
    :items="['California', 'Colorado', 'Florida', 'Georgia', 'Texas', 'Wyoming']"
  />
</template>