Generate flag types (again?)

Closes #1381

flag_timestamp.go

@@ -58,38 +58,6 @@ func (t *Timestamp) Get() interface{} {
 	return *t
 }
 
-// TimestampFlag is a flag with type time
-type TimestampFlag struct {
-	Name        string
-	Aliases     []string
-	Usage       string
-	EnvVars     []string
-	FilePath    string
-	Required    bool
-	Hidden      bool
-	Layout      string
-	Value       *Timestamp
-	DefaultText string
-	HasBeenSet  bool
-	Destination *Timestamp
-}
-
-// IsSet returns whether or not the flag has been set through env or file
-func (f *TimestampFlag) IsSet() bool {
-	return f.HasBeenSet
-}
-
-// String returns a readable representation of this value
-// (for usage defaults)
-func (f *TimestampFlag) String() string {
-	return FlagStringer(f)
-}
-
-// Names returns the names of the flag
-func (f *TimestampFlag) Names() []string {
-	return flagNames(f.Name, f.Aliases)
-}
-
 // IsRequired returns whether or not the flag is required
 func (f *TimestampFlag) IsRequired() bool {
 	return f.Required