Replace render_ce to render in EE template

What does this MR do and why?

For Upstream, there is no need to use render_ce.

In file ee/app/views/projects/_merge_request_settings.html.haml, render_ce and render have the same effect,

because the template files here are all in the app directory, and there is no template with the same name under ee.

The result of find below can prove that:

results of `find` command

cd gitlab

% find . -name '*merge_request_merge_method_settings*'
./app/views/projects/_merge_request_merge_method_settings.html.haml

% find . -name '*merge_request_merge_options_settings*'
./app/views/projects/_merge_request_merge_options_settings.html.haml

 % find . -name '*merge_request_squash_options_settings*'
./app/views/projects/_merge_request_squash_options_settings.html.haml

 % find . -name '*merge_request_merge_checks_settings*'  
./app/views/projects/_merge_request_merge_checks_settings.html.haml


% find . -name '*merge_request_merge_commit_template*'     
./app/views/projects/_merge_request_merge_commit_template.html.haml

 find . -name '*merge_request_squash_commit_template*'
./app/views/projects/_merge_request_squash_commit_template.html.haml

 % find . -name '*merge_request_target_project_settings*'
./app/views/projects/_merge_request_target_project_settings.html.haml

For JH, must use render to override the template

Related JH MR: https://jihulab.com/gitlab-cn/gitlab/-/merge_requests/1711/diffs

jh/app/views/projects/_merge_request_merge_method_settings.html.haml

= render_ee 'projects/merge_request_merge_method_settings', local_assigns

-# Other JH code ...

Use render to allow JH to override the template file merge_request_merge_method_settings and reuse it under JH dir.

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See doc: https://docs.gitlab.com/ee/development/ee_features.html#using-render_ce

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cc JH EM @mtan-gitlab

Screenshots or screen recordings

The project settings page is displayed normally.

http://127.0.0.1:3000/jashkenas/Underscore/-/settings/merge_requests

Before	After (No Changes)

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