Auto merge of #51235 - nikomatsakis:issue-51117-borrowck-implicit-deref, r=eddyb

remove notion of Implicit derefs from mem-cat

`PointerKind` is included in `LoanPath` and hence forms part of the equality check; this led to having two unequal paths that both represent `*x`, depending on whether the `*` was inserted automatically or explicitly. Bad mojo.

Fixes #51117

r? @eddyb