Fix duplicated methods found by RuboCop

Author: eregon

lib/truffle/java/java.rb

@@ -41,8 +41,7 @@ def hash
     def eql?(another)
       Truffle::Interop::Java.java_eql?(@value, @value)
     end
-
-    alias_method :eql?, :==
+    alias_method :==, :eql?
 
     def equal?(another)
       nil != @value and JavaObject === another and @value.equals(another.value)

lib/truffle/java/java_utilities.rb

@@ -367,7 +367,7 @@ def toString
     a_proxy = Module.new do
       define_singleton_method(:included, included_method)
       class << self
-        attr_accessor :java_class
+        attr_writer :java_class
         def java_class
           JavaUtilities::wrap_java_value(@java_class)
         end

src/main/ruby/core/env.rb

@@ -49,6 +49,7 @@ def initialize
     def size
       @variables.size
     end
+    alias_method :length, :size
 
     private def lookup(key)
       value = Truffle::POSIX.getenv(StringValue(key))
@@ -231,14 +232,6 @@ def empty?
       true
     end
 
-    def length
-      sz = 0
-      each { |_k, _v| sz += 1 }
-      sz
-    end
-
-    alias_method :size, :length
-
     def rehash
       # No need to do anything, our keys are always strings
     end