Align "wrong number of arguments" messages

Make "N for M" into the form "given N, expected M".

As I worked, I noticed that the `argnum_error()` function had a part to include the method name in the message.
I think this part is no longer needed by https://github.com/mruby/mruby/pull/5394.

  - Before this patch

    ```console
    % bin/mruby -e '[1, 2, 3].each 0'
    trace (most recent call last):
            [1] -e:1
    -e:1:in each: 'each': wrong number of arguments (1 for 0) (ArgumentError)
    ```

  - After this patch

    ```console
    % bin/mruby -e '[1, 2, 3].each 0'
    trace (most recent call last):
            [1] -e:1
    -e:1:in each: wrong number of arguments (given 1, expected 0) (ArgumentError)
    ```

1 files changed, 1 insertions, 1 deletions

diff --git a/mrblib/string.rb b/mrblib/string.rb
index 2b3178688..81ddf6784 100644
--- a/mrblib/string.rb
+++ b/mrblib/string.rb
@@ -51,7 +51,7 @@ class String
   # ISO 15.2.10.5.18
   def gsub(*args, &block)
     return to_enum(:gsub, *args) if args.length == 1 && !block
-    raise ArgumentError, "wrong number of arguments" unless (1..2).include?(args.length)
+    raise ArgumentError, "wrong number of arguments (given #{args.length}, expected 1..2)" unless (1..2).include?(args.length)
 
     pattern, replace = *args
     plen = pattern.length