test: Remove a needless require

[cosmo0920]

(check all that apply)

• tests added
• tests passing
• README updated (if needed)
• README Table of Contents updated (if needed)
• History.md and version in gemspec are untouched
• backward compatible
• feature works in elasticsearch_dynamic (not required but recommended)

[cosmo0920]

Hmm.., we need to handle these CI failures with more cycles...

[cosmo0920]

@kenhys @daipom Do you all have cycles to handle these CI failures? We need to review the PR #1030. Although, the CI is failing. We have to fix CI errors at first.