[ci skip] Remove some Srting#split samples

mruby not support regexp, so remove these samples.

src/string.c

@@ -1714,10 +1714,8 @@ mrb_str_rindex_m(mrb_state *mrb, mrb_value str)
  *     " now's  the time".split        #=> ["now's", "the", "time"]
  *     " now's  the time".split(' ')   #=> ["now's", "the", "time"]
  *     " now's  the time".split(/ /)   #=> ["", "now's", "", "the", "time"]
- *     "1, 2.34,56, 7".split(%r{,\s*}) #=> ["1", "2.34", "56", "7"]
  *     "hello".split(//)               #=> ["h", "e", "l", "l", "o"]
  *     "hello".split(//, 3)            #=> ["h", "e", "llo"]
- *     "hi mom".split(%r{\s*})         #=> ["h", "i", "m", "o", "m"]
  *
  *     "mellow yellow".split("ello")   #=> ["m", "w y", "w"]
  *     "1,2,,3,4,,".split(',')         #=> ["1", "2", "", "3", "4"]