fix(tui): drop local string-trim/char-whitespace? shadowing scheme's

ober

c4e6f92419d2b9ccf940935ea4390dd0d52721ac

diff --git a/signal/tui/main.ss b/signal/tui/main.ss
index 8ab8a86..a88ce74 100644
--- a/signal/tui/main.ss
+++ b/signal/tui/main.ss
@@ -2984,28 +2984,6 @@
       [(char=? (string-ref input i) #\@) i]
       [else (find-last-at input (- i 1))]))
 
-  (def (string-trim s)
-    (let* ([len (string-length s)]
-           [start (let loop ([i 0])
-                    (if (or (>= i len)
-                            (not (char-whitespace? (string-ref s i))))
-                      i
-                      (loop (+ i 1))))]
-           [end (let loop ([i (- len 1)])
-                  (if (or (< i 0)
-                          (not (char-whitespace? (string-ref s i))))
-                    (+ i 1)
-                    (- i 1)))])
-      (if (>= start end)
-        ""
-        (substring s start end))))
-
-  (def (char-whitespace? ch)
-    (or (char=? ch #\space)
-        (char=? ch #\tab)
-        (char=? ch #\newline)
-        (char=? ch #\return)))
-
   ;; Activate mention mode: gather candidates filtered by the current query.
   (def (activate-mention! state)
     (let* ([input (tui-state-input state)]