Remove duplicated `String#each_char`

mrbgems/mruby-io/test/io.rb

@@ -84,7 +84,7 @@ end
 
 assert('IO#getc', '15.2.20.5.8') do
   io = IO.new(IO.sysopen($mrbtest_io_rfname))
-  $mrbtest_io_msg.each_char { |ch|
+  $mrbtest_io_msg.split("").each { |ch|
     assert_equal ch, io.getc
   }
   assert_equal nil, io.getc
@@ -127,7 +127,7 @@ end
 assert('IO#readchar', '15.2.20.5.15') do
   # almost same as IO#getc
   IO.open(IO.sysopen($mrbtest_io_rfname)) do |io|
-    $mrbtest_io_msg.each_char { |ch|
+    $mrbtest_io_msg.split("").each { |ch|
       assert_equal ch, io.readchar
     }
     assert_raise(EOFError) do

mrbgems/mruby-method/test/method.rb

@@ -21,7 +21,7 @@ class Interpreter
   }
   def interpret(string)
     @ret = ""
-    string.each_char {|b| Dispatcher[b].bind(self).call }
+    string.split("").each {|b| Dispatcher[b].bind(self).call }
   end
 end
 

mrbgems/mruby-string-ext/mrblib/string.rb

@@ -310,11 +310,15 @@ class String
     end
   end
 
+  ##
+  # Call the given block for each character of
+  # +self+.
   def each_char(&block)
     return to_enum :each_char unless block
-
-    split('').each do |i|
-      block.call(i)
+    pos = 0
+    while pos < self.size
+      block.call(self[pos])
+      pos += 1
     end
     self
   end

mrbgems/mruby-string-ext/test/string.rb

@@ -657,19 +657,19 @@ assert('String#chars(UTF-8)') do
 end if UTF8STRING
 
 assert('String#each_char') do
-  s = ""
+  chars = []
   "hello!".each_char do |x|
-    s += x
+    chars << x
   end
-  assert_equal "hello!", s
+  assert_equal ["h", "e", "l", "l", "o", "!"], chars
 end
 
 assert('String#each_char(UTF-8)') do
-  s = ""
+  chars = []
   "こんにちは世界!".each_char do |x|
-    s += x
+    chars << x
   end
-  assert_equal "こんにちは世界!", s
+  assert_equal ["こ", "ん", "に", "ち", "は", "世", "界", "!"], chars
 end if UTF8STRING
 
 assert('String#codepoints') do

mrblib/string.rb

@@ -164,18 +164,6 @@ class String
     self.replace(str)
   end
 
-  ##
-  # Call the given block for each character of
-  # +self+.
-  def each_char(&block)
-    pos = 0
-    while pos < self.size
-      block.call(self[pos])
-      pos += 1
-    end
-    self
-  end
-
   ##
   # Call the given block for each byte of +self+.
   def each_byte(&block)