gh-88886: Remove excessive encoding name normalization (GH-137167)

The codecs lookup function now performs only minimal normalization of
the encoding name before passing it to the search functions:
all ASCII letters are converted to lower case, spaces are replaced
with hyphens.

Excessive normalization broke third-party codecs providers, like
python-iconv.

Revert "bpo-37751: Fix codecs.lookup() normalization (GH-15092)"

This reverts commit 20f59fe1f7748ae899aceee4cb560e5e1f528a1f.