feat: Delete bulkActionsMixin (#9800)

# Pull Request Template

## Description

This PR will remove the `bulkActionsMixin` usage. Seems like it is not
used anywhere.

Fixes https://linear.app/chatwoot/issue/CW-3453/delete-bulkactionsmixin

## Type of change

- [x] New feature (non-breaking change which adds functionality)


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/javascript/dashboard/mixins/bulkActionsMixin.js

@@ -1,15 +0,0 @@
-export default {
-  props: {
-    trianglePosition: {
-      type: String,
-      default: '0',
-    },
-  },
-  computed: {
-    cssVars() {
-      return {
-        '--triangle-position': this.trianglePosition + 'rem',
-      };
-    },
-  },
-};

app/javascript/dashboard/mixins/specs/bulkActions.spec.js

@@ -1,19 +0,0 @@
-import { mount } from '@vue/test-utils';
-import bulkActionsMixin from '../bulkActionsMixin';
-describe('bulkActionsMixin', () => {
-  it('returns the prop and computed values for triangle position:', async () => {
-    const Component = {
-      render() {},
-      title: 'MyComponent',
-      mixins: [bulkActionsMixin],
-    };
-    const wrapper = mount(Component);
-    await wrapper.setProps({
-      trianglePosition: '10',
-    });
-    expect(wrapper.props().trianglePosition).toEqual('10');
-    expect(wrapper.vm.cssVars).toEqual({
-      '--triangle-position': '10rem',
-    });
-  });
-});