Remove `tests/run-make-fulldeps/pretty-expanded`

This was an ancient regression test for #12685, caused by `-Zunpretty=expanded`
crashing on certain code produced by `#[derive(RustcEncodable)]`.

tests/run-make-fulldeps/pretty-expanded/Makefile

@@ -1,4 +0,0 @@
-include ../../run-make/tools.mk
-
-all:
-	$(RUSTC) -o $(TMPDIR)/input.expanded.rs -Zunpretty=expanded input.rs

tests/run-make-fulldeps/pretty-expanded/input.rs

@@ -1,25 +0,0 @@
-// #13544
-
-#[derive(Debug)]
-pub struct A;
-
-#[derive(Debug)]
-pub struct B(isize);
-
-#[derive(Debug)]
-pub struct C {
-    x: isize,
-}
-
-#[derive(Debug)]
-pub enum D {}
-
-#[derive(Debug)]
-pub enum E {
-    y,
-}
-
-#[derive(Debug)]
-pub enum F {
-    z(isize),
-}