Move GlIcon import from mixin to components

The vue_shared/mixins/related_issuable_mixin.js exposed a component
import to the mixin consumers. This is a bad pattern, as there is a
disconnect between templates of the components utilizing the mixin and
the components they import. This is moving the import to the actual
components.

app/assets/javascripts/vue_shared/mixins/related_issuable_mixin.js

@@ -2,7 +2,6 @@ import { isEmpty } from 'lodash';
 import { sprintf, __ } from '~/locale';
 import { formatDate } from '~/lib/utils/datetime_utility';
 import tooltip from '~/vue_shared/directives/tooltip';
-import icon from '~/vue_shared/components/icon.vue';
 import timeagoMixin from '~/vue_shared/mixins/timeago';
 
 const mixins = {
@@ -100,9 +99,6 @@ const mixins = {
       default: () => ({}),
     },
   },
-  components: {
-    icon,
-  },
   directives: {
     tooltip,
   },

ee/app/assets/javascripts/related_issues/components/issue_token.vue

 <script>
+import { GlIcon } from '@gitlab/ui';
 import { __, sprintf } from '~/locale';
 import relatedIssuableMixin from '~/vue_shared/mixins/related_issuable_mixin';
 
 export default {
   name: 'IssueToken',
+  components: {
+    GlIcon,
+  },
   mixins: [relatedIssuableMixin],
   props: {
     isCondensed: {
@@ -78,7 +82,7 @@ export default {
           'issuable-info': !isCondensed,
         }"
       >
-        <icon
+        <gl-icon
           v-if="hasState"
           v-tooltip
           :class="iconClass"