11877: fix: splitting path of a glob import wrongly adds `self` r=Veykril a=iDawer
Close #11703
`ast::UseTree::split_prefix` handles globs now.
Removed an extra branch for globs in `ide_db::imports::merge_imports::recursive_merge` (superseeded by split_prefix).
Co-authored-by: iDawer <ilnur.iskhakov.oss@outlook.com>
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