Remove static keyword from vshReadline when readline does not exist

This patch removes the static keyword from the vshReadline which was
introduced in commit 834c5720. With
readline the vshReadline function is not static but when compiling
without readline it was defined as static which caused compilation
error.

tools/vsh.c

@@ -2655,7 +2655,7 @@ vshReadlineDeinit(vshControl *ctl ATTRIBUTE_UNUSED)
     /* empty */
 }
 
-static char *
+char *
 vshReadline(vshControl *ctl, const char *prompt)
 {
     char line[1024];