Remove tensorflow/keras files and the keras dependency

[priya-sundaram-dev]

Closes the cleanup discussed in #15418.

These four files aren't algorithms — they're how-to-use scripts that wrap a deep-learning framework, and they were the only thing dragging in the heavy keras/tensorflow stack:

• computer_vision/cnn_classification.py
• dynamic_programming/k_means_clustering_tensorflow.py
• machine_learning/lstm/lstm_prediction.py
• neural_network/input_data.py — a TensorFlow MNIST data loader; git grep confirms nothing under a collected .py path imports it.

I also removed the now-orphaned machine_learning/lstm/ package (only __init__.py + sample_data.csv, which existed solely for lstm_prediction.py).

Cleanups

• Dropped keras>=3.7 from pyproject.toml and ran uv sync --upgrade && uv lock. The lock now resolves 80 packages; removed absl-py, h5py, keras, ml-dtypes, namex, optree (plus minor bumps to fonttools/httpcore2/httpx2 from --upgrade).
• Removed the # keras needs hdf5 on pre-release Python libhdf5-dev install step from both build.yml and sphinx.yml — it only existed for keras.
• Dropped the four now-dead --ignore= entries in build.yml.
• Removed the four DIRECTORY.md entries and the empty Lstm heading.

Verification

• git grep -i -E 'tensorflow|keras' now returns only English dictionary words in strings/anagrams.txt / strings/words.txt (kerasin/kerasine), never the library.
• Both workflow files still parse as valid YAML.

One thing left in place

neural_network/gan.py_tf still import input_data, but its .py_tf extension means it is not collected or executed anywhere, and it's out of scope for this PR. Happy to remove or restore it separately if you'd like.

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Describe your change

• Fix a bug or typo in an existing algorithm? — housekeeping: removes non-algorithm how-to files and the dead keras/tensorflow dependency they dragged in (per Should we remove dependencies keras and tensorflow? #15418).
• Documentation change? — updates DIRECTORY.md.

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. — N/A: this is a coordinated removal of four non-algorithm files + the orphaned lstm/ package, as agreed in Should we remove dependencies keras and tensorflow? #15418.
• All new Python files are placed inside an existing directory. — N/A (no new files).
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints. — N/A (removal-only).
• All functions have doctests that pass the automated testing. — N/A (removal-only).
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation. — N/A (removal-only).

[algorithms-keeper]

Closing this pull request as invalid

@priya-sundaram-dev, this pull request is being closed as none of the checkboxes have been marked. It is important that you go through the checklist and mark the ones relevant to this pull request. Please read the Contributing guidelines.

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• If it is, then mark it by putting a x between the square bracket like so: [x]

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[priya-sundaram-dev]

Reopened as #15420 with the checklist filled in (the keeper bot auto-closed this one because none of the template boxes were marked — my oversight, since it's a coordinated removal PR rather than a single-algorithm add). Continuing there.