Remove @_typeSequence attribute

This is no longer needed now that we have the
ellipsis spelling.

Author: hamishknight

Sources/SwiftParser/Lookahead.swift

@@ -250,7 +250,6 @@ extension Parser.Lookahead {
     "async",
     "Sendable",
     "unchecked",
-    "_typeSequence",
     "_local",
     "block_storage",
     "box",

gyb_syntax_support/AttributeKinds.py

@@ -134,7 +134,6 @@ def __init__(self, name, swift_name=None):
     TypeAttribute('async'),
     TypeAttribute('Sendable'),
     TypeAttribute('unchecked'),
-    TypeAttribute('_typeSequence'),
     TypeAttribute('_local'),
     TypeAttribute('_noMetadata'),
 
@@ -393,12 +392,7 @@ def __init__(self, name, swift_name=None):
                   NotSerialized,
                   ABIStableToAdd,  ABIStableToRemove,  APIStableToAdd,  APIStableToRemove,
                   code=70),
-    DeclAttribute('_typeSequence', 'TypeSequence',
-                  OnGenericTypeParam,
-                  UserInaccessible,
-                  NotSerialized,
-                  ABIBreakingToAdd,  ABIBreakingToRemove,  APIBreakingToAdd,  APIBreakingToRemove,
-                  code=71),
+  # NOTE: 71 is unused
   # NOTE: 72 is unused
     DeclAttribute('_optimize', 'Optimize',
                   OnAbstractFunction,  OnSubscript,  OnVar,