Help: Remove outdated statement about get_filename_component()

After !2853, the statement that the "longest file extension is
always considered" is no longer true. Both NAME_WLE and
LAST_EXT now return details based on the shortest file
extension.

Fixes: 7a25ef32 (Help: Add documentation for new get_filename_component components, 2019-01-24, 3.14.0-rc1)
13 jobs for get_filename_component_docs
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