Remove #to_sym calls from Drop and Variable

Symbols are not needed here and using plain strings is nicer on Ruby

test/liquid/variable_test.rb

@@ -11,71 +11,71 @@ class VariableTest < Test::Unit::TestCase
   def test_filters
     var = Variable.new('hello | textileze')
     assert_equal 'hello', var.name
-    assert_equal [[:textileze,[]]], var.filters
+    assert_equal [["textileze",[]]], var.filters
 
     var = Variable.new('hello | textileze | paragraph')
     assert_equal 'hello', var.name
-    assert_equal [[:textileze,[]], [:paragraph,[]]], var.filters
+    assert_equal [["textileze",[]], ["paragraph",[]]], var.filters
 
     var = Variable.new(%! hello | strftime: '%Y'!)
     assert_equal 'hello', var.name
-    assert_equal [[:strftime,["'%Y'"]]], var.filters
+    assert_equal [["strftime",["'%Y'"]]], var.filters
 
     var = Variable.new(%! 'typo' | link_to: 'Typo', true !)
     assert_equal %!'typo'!, var.name
-    assert_equal [[:link_to,["'Typo'", "true"]]], var.filters
+    assert_equal [["link_to",["'Typo'", "true"]]], var.filters
 
     var = Variable.new(%! 'typo' | link_to: 'Typo', false !)
     assert_equal %!'typo'!, var.name
-    assert_equal [[:link_to,["'Typo'", "false"]]], var.filters
+    assert_equal [["link_to",["'Typo'", "false"]]], var.filters
 
     var = Variable.new(%! 'foo' | repeat: 3 !)
     assert_equal %!'foo'!, var.name
-    assert_equal [[:repeat,["3"]]], var.filters
+    assert_equal [["repeat",["3"]]], var.filters
 
     var = Variable.new(%! 'foo' | repeat: 3, 3 !)
     assert_equal %!'foo'!, var.name
-    assert_equal [[:repeat,["3","3"]]], var.filters
+    assert_equal [["repeat",["3","3"]]], var.filters
 
     var = Variable.new(%! 'foo' | repeat: 3, 3, 3 !)
     assert_equal %!'foo'!, var.name
-    assert_equal [[:repeat,["3","3","3"]]], var.filters
+    assert_equal [["repeat",["3","3","3"]]], var.filters
 
     var = Variable.new(%! hello | strftime: '%Y, okay?'!)
     assert_equal 'hello', var.name
-    assert_equal [[:strftime,["'%Y, okay?'"]]], var.filters
+    assert_equal [["strftime",["'%Y, okay?'"]]], var.filters
 
     var = Variable.new(%! hello | things: "%Y, okay?", 'the other one'!)
     assert_equal 'hello', var.name
-    assert_equal [[:things,["\"%Y, okay?\"","'the other one'"]]], var.filters
+    assert_equal [["things",["\"%Y, okay?\"","'the other one'"]]], var.filters
   end
 
   def test_filter_with_date_parameter
 
     var = Variable.new(%! '2006-06-06' | date: "%m/%d/%Y"!)
     assert_equal "'2006-06-06'", var.name
-    assert_equal [[:date,["\"%m/%d/%Y\""]]], var.filters
+    assert_equal [["date",["\"%m/%d/%Y\""]]], var.filters
 
   end
 
   def test_filters_without_whitespace
     var = Variable.new('hello | textileze | paragraph')
     assert_equal 'hello', var.name
-    assert_equal [[:textileze,[]], [:paragraph,[]]], var.filters
+    assert_equal [["textileze",[]], ["paragraph",[]]], var.filters
 
     var = Variable.new('hello|textileze|paragraph')
     assert_equal 'hello', var.name
-    assert_equal [[:textileze,[]], [:paragraph,[]]], var.filters
+    assert_equal [["textileze",[]], ["paragraph",[]]], var.filters
 
     var = Variable.new("hello|replace:'foo','bar'|textileze")
     assert_equal 'hello', var.name
-    assert_equal [[:replace, ["'foo'", "'bar'"]], [:textileze, []]], var.filters
+    assert_equal [["replace", ["'foo'", "'bar'"]], ["textileze", []]], var.filters
   end
 
   def test_symbol
     var = Variable.new("http://disney.com/logo.gif | image: 'med' ")
     assert_equal 'http://disney.com/logo.gif', var.name
-    assert_equal [[:image,["'med'"]]], var.filters
+    assert_equal [["image",["'med'"]]], var.filters
   end
 
   def test_string_single_quoted