Remove auto_cast from field_flags

- auto_cast is parsed as its own expression

core/odin/ast/ast.odin

@@ -584,7 +584,6 @@ Field_Flag :: enum {
 	Using,
 	No_Alias,
 	C_Vararg,
-	Auto_Cast,
 	Const,
 	Any_Int,
 	Subtype,
@@ -604,7 +603,6 @@ field_flag_strings := [Field_Flag]string{
 	.Using              = "using",
 	.No_Alias           = "#no_alias",
 	.C_Vararg           = "#c_vararg",
-	.Auto_Cast          = "auto_cast",
 	.Const              = "#const",
 	.Any_Int            = "#any_int",
 	.Subtype            = "#subtype",
@@ -641,7 +639,6 @@ Field_Flags_Signature :: Field_Flags{
 	.No_Alias,
 	.C_Vararg,
 	.Const,
-	.Auto_Cast,
 	.Any_Int,
 	.By_Ptr,
 	.Default_Parameters,