Remove Duplicate Declaration of pandas in Dockerfile (#6959)

### Description

This pull request removes the redundant installation of `pandas` from
the `Dockerfile`.
It was previously declared twice, and this update eliminates the
duplicate entry, improving the clarity and maintainability of the
`Dockerfile`.


https://github.com/microsoft/DeepSpeed/blob/018ece5af2d89a11a4a235f81f94496c78b4f990/docker/Dockerfile#L124


https://github.com/microsoft/DeepSpeed/blob/018ece5af2d89a11a4a235f81f94496c78b4f990/docker/Dockerfile#L135

### Changes

Removed the duplicate pandas installation line from the `RUN pip
install` command.

docker/Dockerfile

@@ -132,7 +132,6 @@ RUN pip install psutil \
         sentencepiece \
         msgpack \
         requests \
-        pandas \
         sphinx \
         sphinx_rtd_theme \
         scipy \