DOC: fix redundant phrasing in reshaping.rst

[dinesh-git17]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
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Description

Fixes redundant phrasing in the melt section of the reshaping documentation.

Current:

"by setting the ignore_index=False parameter to False"

Fixed:

"by setting the ignore_index parameter to False"

The original text redundantly states ignore_index=False and then says to set it to False.

[mroeschke]

Thanks @dinesh-git17