Also erase substs for new infcx in pin move error

The code originally correctly erased the regions of the type it passed
to the newly created infcx. But after the `fn_sig` query was made to
return an `EarlyBinder<T>`, some substs that were around were
substituted there without erasing their regions. They were then passed
into the newly cerated infcx, which caused the ICE.

tests/ui/moves/pin-mut-reborrow-infer-var-issue-107419.fixed

@@ -0,0 +1,11 @@
+// run-rustfix
+use std::pin::Pin;
+
+fn foo(_: &mut ()) {}
+
+fn main() {
+    let mut uwu = ();
+    let mut r = Pin::new(&mut uwu);
+    foo(r.as_mut().get_mut());
+    foo(r.get_mut()); //~ ERROR use of moved value
+}

tests/ui/moves/pin-mut-reborrow-infer-var-issue-107419.rs

@@ -0,0 +1,11 @@
+// run-rustfix
+use std::pin::Pin;
+
+fn foo(_: &mut ()) {}
+
+fn main() {
+    let mut uwu = ();
+    let mut r = Pin::new(&mut uwu);
+    foo(r.get_mut());
+    foo(r.get_mut()); //~ ERROR use of moved value
+}

tests/ui/moves/pin-mut-reborrow-infer-var-issue-107419.stderr

@@ -0,0 +1,20 @@
+error[E0382]: use of moved value: `r`
+  --> $DIR/pin-mut-reborrow-infer-var-issue-107419.rs:10:9
+   |
+LL |     let mut r = Pin::new(&mut uwu);
+   |         ----- move occurs because `r` has type `Pin<&mut ()>`, which does not implement the `Copy` trait
+LL |     foo(r.get_mut());
+   |           --------- `r` moved due to this method call
+LL |     foo(r.get_mut());
+   |         ^ value used here after move
+   |
+note: `Pin::<&'a mut T>::get_mut` takes ownership of the receiver `self`, which moves `r`
+  --> $SRC_DIR/core/src/pin.rs:LL:COL
+help: consider reborrowing the `Pin` instead of moving it
+   |
+LL |     foo(r.as_mut().get_mut());
+   |           +++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0382`.