fix(VDialog): remove console error on escape keypress

[kuromoka]

Description

removed [Vuetify] No activator found error on escape keypress when dialog is active.

Motivation and Context

fixes #7008

How Has This Been Tested?

visually

Markup:

<template>
  <v-app>
    <v-content>
      <v-layout row justify-center>
        <v-btn
          color="primary"
          dark
          @click.stop="dialog = true"
        >
          Open Dialog
        </v-btn>
        <v-dialog
          v-model="dialog"
          max-width="290"
        >
          <v-card>
            <v-card-title class="headline">Use Google's location service?</v-card-title>
            <v-card-text>
              Let Google help apps determine location. This means sending anonymous location data to Google, even when no apps are running.
            </v-card-text>
            <v-card-actions>
              <v-spacer />
              <v-btn
                color="green darken-1"
                flat="flat"
                @click="dialog = false"
              >
                Disagree
              </v-btn>
              <v-btn
                color="green darken-1"
                flat="flat"
                @click="dialog = false"
              >
                Agree
              </v-btn>
            </v-card-actions>
          </v-card>
        </v-dialog>
      </v-layout>
    </v-content>
  </v-app>
</template>

<script>
  export default {
    data () {
      return {
        dialog: false
      }
    }
  }
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature but make things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and breaking changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)

[codecov]

Codecov Report

Merging #7030 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #7030      +/-   ##
==========================================
+ Coverage    85.3%   85.43%   +0.12%     
==========================================
  Files         298      298              
  Lines        7221     7221              
  Branches     1804     1804              
==========================================
+ Hits         6160     6169       +9     
+ Misses        960      956       -4     
+ Partials      101       96       -5

Impacted Files	Coverage Δ
packages/vuetify/src/components/VDialog/VDialog.js	71.28% <100%> (+7.92%)	⬆️
packages/vuetify/src/mixins/overlayable.ts	41.05% <0%> (+1.05%)	⬆️

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[dsseng]

Looks good