docs: fix docstring parameter names that do not match signatures

[simpleqt]

Docstring-only fixes, each verified against the signature directly above it (found via an AST docstring-Args vs signature sweep over src/diffusers/pipelines):

1. FluxControlNetPipeline.encode_prompt documented a clip_skip parameter — copy-paste from SD-style docs; flux has no CLIP layer-skipping and the parameter does not exist.
2. HunyuanVideo15Pipeline / ...Image2VideoPipeline: the docstring said num_images_per_prompt (int) while the parameter is num_videos_per_prompt.
3. Kandinsky5 _encode_prompt_qwen / _encode_prompt_clip: documented num_videos_per_prompt, which neither helper accepts; removed the stale entries.

Docstrings only; no code change.

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[github-actions]

Hi @simpleqt, thanks for the PR! It does not appear to link an issue it fixes. If this PR addresses an existing issue, please add a closing keyword (e.g. Fixes #1234) to the PR description so the issue is linked. See the contribution guide for more details. If this PR intentionally does not fix a tracked issue, a maintainer can add the no-issue-needed label to silence this reminder.

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[simpleqt]

Closing — pooled into #14715 combined docs PR to reduce review overhead. All fixes are preserved in the combined branch.

[simpleqt]

Correction: my closing comment pointed to #14715 — that number was wrong. The live pooled PR is #14757 (all fixes preserved there, now rebased onto current main).