Remove duplicate lex tests

`RipperTest` already does this (added in #3849)
Since it doesn't use the token classes, it also lists out all the excludes instead of just claiming some are passing.

Author: Earlopain

test/prism/lex_test.rb

@@ -6,43 +6,6 @@
 
 module Prism
   class LexTest < TestCase
-    except = [
-      # https://bugs.ruby-lang.org/issues/21756
-      "spanning_heredoc.txt",
-      # Prism emits a single string in some cases when ripper splits them up
-      "whitequark/dedenting_heredoc.txt",
-      "heredocs_with_fake_newlines.txt",
-      # Prism emits BEG for `on_regexp_end`
-      "spanning_heredoc_newlines.txt",
-    ]
-
-    if RUBY_VERSION < "3.3.0"
-      # This file has changed behavior in Ripper in Ruby 3.3, so we skip it if
-      # we're on an earlier version.
-      except << "seattlerb/pct_w_heredoc_interp_nested.txt"
-
-      # Ruby < 3.3.0 cannot parse heredocs where there are leading whitespace
-      # characters in the heredoc start.
-      # Example: <<~'   EOF' or <<-'  EOF'
-      # https://bugs.ruby-lang.org/issues/19539
-      except << "heredocs_leading_whitespace.txt"
-      except << "whitequark/ruby_bug_19539.txt"
-
-      # https://bugs.ruby-lang.org/issues/19025
-      except << "whitequark/numparam_ruby_bug_19025.txt"
-      # https://bugs.ruby-lang.org/issues/18878
-      except << "whitequark/ruby_bug_18878.txt"
-      # https://bugs.ruby-lang.org/issues/19281
-      except << "whitequark/ruby_bug_19281.txt"
-    end
-
-    # https://bugs.ruby-lang.org/issues/21168#note-5
-    except << "command_method_call_2.txt"
-
-    Fixture.each_for_current_ruby(except: except) do |fixture|
-      define_method(fixture.test_name) { assert_lex(fixture) }
-    end
-
     def test_lex_file
       assert_nothing_raised do
         Prism.lex_file(__FILE__)
@@ -83,16 +46,11 @@ def test_parse_lex_file
       end
     end
 
-    private
-
-    def assert_lex(fixture)
-      source = fixture.read
-
-      result = Prism.lex_compat(source, version: "current")
-      assert_equal [], result.errors
-
-      Prism.lex_ripper(source).zip(result.value).each do |(ripper, prism)|
-        assert_equal ripper, prism
+    if RUBY_VERSION >= "3.3"
+      def test_lex_compare
+        prism = Prism.lex_compat(File.read(__FILE__), version: "current").value
+        ripper = Prism.lex_ripper(File.read(__FILE__))
+        assert_equal(ripper, prism)
       end
     end
   end