Revert "Lex XPath axes without a node test."

Upon further investigation this change turned out to be useless. Nokogiri/libxml
does not allow the use of long axes without tests, instead it ends up
lexing/parsing such a value as a simple node test.

This reverts commit f699b0d097.

lib/oga/xpath/lexer.rl

@@ -219,7 +219,11 @@ module Oga
           | 'parent'
           | 'preceding'
           | 'preceding-sibling'
-          | 'self');
+          | 'self') '::';
+
+        action emit_axis_full {
+          emit(:T_AXIS, ts, te - 2)
+        }
 
         # Short Axes
         #
@@ -302,10 +306,7 @@ module Oga
           string     => emit_string;
           integer    => emit_integer;
           float      => emit_float;
-
+          axis_full  => emit_axis_full;
-          axis_full      => { emit(:T_AXIS, ts, te) };
-          axis_full '::' => { emit(:T_AXIS, ts, te - 2) };
-
           axis_short => emit_axis_short;
           identifier => emit_identifier;
         *|;

spec/oga/xpath/parser/axes_spec.rb

@@ -44,21 +44,6 @@ describe Oga::XPath::Parser do
       )
     end
 
-    example 'parse the descendant-or-self axis without a test' do
-      parse_xpath('/descendant-or-self').should == s(
-        :absolute_path,
-        s(:axis, 'descendant-or-self')
-      )
-    end
-
-    example 'parse the descendant-or-self axis followed by an attribute axis' do
-      parse_xpath('/descendant-or-self/attribute::foo').should == s(
-        :absolute_path,
-        s(:axis, 'descendant-or-self'),
-        s(:axis, 'attribute', s(:test, nil, 'foo'))
-      )
-    end
-
     example 'parse the following axis' do
       parse_xpath('/following::A').should == s(
         :absolute_path,