Get rid of obsoleted RJITFirst

It was renamed from test_mjit, but we did not maintain it as test_rjit.
We test RJIT very differently.

tool/lib/test/unit.rb

@@ -53,17 +53,7 @@ def group(list)
         end
       end
 
-      module RJITFirst
-        def group(list)
-          # RJIT first
-          rjit, others = list.partition {|e| /test_rjit/ =~ e}
-          rjit + others
-        end
-      end
-
       class Alpha < NoSort
-        include RJITFirst
-
         def sort_by_name(list)
           list.sort_by(&:name)
         end
@@ -76,8 +66,6 @@ def sort_by_string(list)
 
       # shuffle test suites based on CRC32 of their names
       Shuffle = Struct.new(:seed, :salt) do
-        include RJITFirst
-
         def initialize(seed)
           self.class::CRC_TBL ||= (0..255).map {|i|
             (0..7).inject(i) {|c,| (c & 1 == 1) ? (0xEDB88320 ^ (c >> 1)) : (c >> 1) }
@@ -95,6 +83,10 @@ def sort_by_string(list)
           list.sort_by {|e| randomize_key(e)}
         end
 
+        def group(list)
+          list
+        end
+
         private
 
         def crc32(str, crc32 = 0xffffffff)