Remove the fn pointer #[track_caller] test.

The ICE stderr isn't normalizing correctly on some builders.

src/test/ui/rfc-2091-track-caller/taking-fn-pointer.rs

-// failure-status: 101
-// normalize-stderr-test "note: rustc 1.* running on .*" -> "note: rustc VERSION running on TARGET"
-// normalize-stderr-test "note: compiler flags: .*" -> "note: compiler flags: FLAGS"
-
-#![feature(track_caller)] //~ WARN the feature `track_caller` is incomplete
-
-#[track_caller]
-fn f() {}
-
-fn call_it(x: fn()) {
-    x();
-}
-
-fn main() {
-    call_it(f);
-}

src/test/ui/rfc-2091-track-caller/taking-fn-pointer.stderr

-warning: the feature `track_caller` is incomplete and may cause the compiler to crash
-  --> $DIR/taking-fn-pointer.rs:5:12
-   |
-LL | #![feature(track_caller)]
-   |            ^^^^^^^^^^^^
-   |
-   = note: `#[warn(incomplete_features)]` on by default
-
-thread 'rustc' panicked at 'index out of bounds: the len is 1 but the index is 1', $SRC_DIR/libcore/slice/mod.rs:LL:COL
-note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
-
-error: internal compiler error: unexpected panic
-
-note: the compiler unexpectedly panicked. this is a bug.
-
-note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
-
-note: rustc VERSION running on TARGET
-
-note: compiler flags: FLAGS
-