Update comment in test which has changed its purpose

Author: Mark-Simulacrum

src/test/ui/parser/regions-out-of-scope-slice.rs

@@ -1,8 +1,6 @@
-// blk region isn't supported in the front-end
+// This basically tests the parser's recovery on `'blk` in the wrong place.
 
 fn foo(cond: bool) {
-    // Here we will infer a type that uses the
-    // region of the if stmt then block, but in the scope:
     let mut x;
 
     if cond {

src/test/ui/parser/regions-out-of-scope-slice.stderr

@@ -1,5 +1,5 @@
 error: expected `:`, found `[`
-  --> $DIR/regions-out-of-scope-slice.rs:9:19
+  --> $DIR/regions-out-of-scope-slice.rs:7:19
    |
 LL |         x = &'blk [1,2,3]; //~ ERROR expected `:`, found `[`
    |                   ^ expected `:`