Remove BATCH_SIZE from WikiFileFinder

What does this MR do?

It removes BATCH_SIZE from WikiFileFinder as it is not needed.

There are no performance problems observed

• created 45000 wiki pages, 21000 of them were for a project used for searching (id = 8)
• searched for a string that was present in multiple wiki pages, only few wiki pages and no wiki page
• tested with BATCH_SIZE - load time around 2-3 s
• tested without BATCH_SIZE - load time remained same

What are the relevant issue numbers?

Closes #57223 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer