Remove loadHTMLFixture usage in `spec/frontend/`

Description

This issue is part of Replace loadHTMLFixture with static imports (&10244 - closed). Let's replace references to loadHTMLFixture in the following places:

• spec/frontend/activities_spec.js:42: loadHTMLFixture(fixtureTemplate);
• spec/frontend/awards_handler_spec.js:89: loadHTMLFixture('snippets/show.html');
• spec/frontend/bootstrap_linked_tabs_spec.js:6: loadHTMLFixture('static/linked_tabs.html');
• spec/frontend/create_item_dropdown_spec.js:45: loadHTMLFixture('static/create_item_dropdown.html');
• spec/frontend/deprecated_jquery_dropdown_spec.js:68: loadHTMLFixture('static/deprecated_jquery_dropdown.html');
• spec/frontend/dropzone_input_spec.js:51: loadHTMLFixture('milestones/new-milestone.html');
• spec/frontend/gl_field_errors_spec.js:13: loadHTMLFixture('static/gl_field_errors.html');
• spec/frontend/header_spec.js:26: loadHTMLFixture(fixtureTemplate);
• spec/frontend/merge_request_spec.js:19: loadHTMLFixture('merge_requests/merge_request_with_task_list.html');
• spec/frontend/merge_request_spec.js:115: loadHTMLFixture('merge_requests/merge_request_of_current_user.html');
• spec/frontend/merge_request_tabs_spec.js:87: loadHTMLFixture('merge_requests/merge_request_with_task_list.html');
• spec/frontend/new_branch_spec.js:23: loadHTMLFixture('branches/new_branch.html');
• spec/frontend/oauth_remember_me_spec.js:11: loadHTMLFixture('static/oauth_remember_me.html');
• spec/frontend/read_more_spec.js:15: loadHTMLFixture(fixtureName);
• spec/frontend/right_sidebar_spec.js:33: loadHTMLFixture(fixtureName);
• spec/frontend/settings_panels_spec.js:7: loadHTMLFixture('groups/edit.html');
• spec/frontend/shortcuts_spec.js:25: loadHTMLFixture(fixtureName);
• spec/frontend/user_popovers_spec.js:43: loadHTMLFixture(fixtureTemplate);
• spec/frontend/zen_mode_spec.js:40: loadHTMLFixture(fixtureName);

Implementation Guide

Please see the parent epic for reasoning and examples of how to do this. If you'd like to pick up this issue, please leave a comment so that others do not pick it up :)