Don't show "⟦tail⟧" and "tail" annotations

These turned out to be too "noisy".

(Even if we wanted to show these, optionally, the Emacs front end
could add these -- they don't need to be "baked into" the annotation
strings prepared by the back end. I'm not adding such a customization
with this commit; too many options is its own kind of "noise".)

We do still highlight them with the two racket-xp-tail-* faces.

doc/racket-mode.texi

@@ -1283,18 +1283,16 @@ x
 
 When point is on the opening parenthesis of an expression in tail
 position, it is highlighted using the face
-@ref{racket-xp-tail-position-face} and has a tooltip annotation,
-``tail''.
+@ref{racket-xp-tail-position-face}.
 
 When point is on the opening parenthesis of an enclosing
 expression with respect to which one or more expressions are in
 tail position, it is highlighted using the face
-@ref{racket-xp-tail-target-face} and has a tooltip annotation,
-"⟦tail⟧".
+@ref{racket-xp-tail-target-face}.
 
 Furthermore, when point is on the opening parenthesis of either
 kind of expression, all of the immediately related expressions
-are also highlighted. Various commands to move among them:
+are also highlighted. Various commands move among them:
 
 @itemize
 @item

racket-xp.el

@@ -188,18 +188,16 @@ understands the two different imports of \"define\":
 
 When point is on the opening parenthesis of an expression in tail
 position, it is highlighted using the face
-`racket-xp-tail-position-face' and has a tooltip annotation,
-\"tail\".
+`racket-xp-tail-position-face'.
 
 When point is on the opening parenthesis of an enclosing
 expression with respect to which one or more expressions are in
 tail position, it is highlighted using the face
-`racket-xp-tail-target-face' and has a tooltip annotation,
-\"⟦tail⟧\".
+`racket-xp-tail-target-face'.
 
 Furthermore, when point is on the opening parenthesis of either
 kind of expression, all of the immediately related expressions
-are also highlighted. Various commands to move among them:
+are also highlighted. Various commands move among them:
 
   - `racket-xp-tail-up'
   - `racket-xp-tail-down'

racket/commands/check-syntax.rkt

@@ -176,9 +176,7 @@
          (hash-update! ht-tails
                        (add1 head)
                        (λ (v) (set-add v (add1 tail)))
-                       (set))
-         (send this syncheck:add-mouse-over-status "" head (add1 head) "⟦tail⟧")
-         (send this syncheck:add-mouse-over-status "" tail (add1 tail) "tail")]
+                       (set))]
         [[_ _ _]
          (log-racket-mode-warning
           "Ignoring syncheck:add-tail-arrow because sources differ"