goose: remove optional directive

This introduces some short-term pain in practice, but I aim to fix that
with the goose.Value directive.

Reviewed-by: Tuo Shan <shantuo@google.com>

internal/goose/testdata/OptionalMissing/foo/foo.go

@@ -1,16 +0,0 @@
-package main
-
-import "fmt"
-
-func main() {
-	fmt.Println(injectBar())
-}
-
-type foo int
-type bar int
-
-//goose:provide
-//goose:optional f
-func provideBar(f foo) bar {
-	return bar(f)
-}

internal/goose/testdata/OptionalMissing/foo/foo_goose.go

@@ -1,7 +0,0 @@
-//+build gooseinject
-
-package main
-
-//goose:use provideBar
-
-func injectBar() bar

internal/goose/testdata/OptionalMissing/out.txt

@@ -1 +0,0 @@
-0

internal/goose/testdata/OptionalMissing/pkg

@@ -1 +0,0 @@
-foo

internal/goose/testdata/OptionalPresent/foo/foo.go

@@ -1,16 +0,0 @@
-package main
-
-import "fmt"
-
-func main() {
-	fmt.Println(injectBar(42))
-}
-
-type foo int
-type bar int
-
-//goose:provide
-//goose:optional f
-func provideBar(f foo) bar {
-	return bar(f)
-}

internal/goose/testdata/OptionalPresent/foo/foo_goose.go

@@ -1,7 +0,0 @@
-//+build gooseinject
-
-package main
-
-//goose:use provideBar
-
-func injectBar(foo) bar

internal/goose/testdata/OptionalPresent/out.txt

@@ -1 +0,0 @@
-42

internal/goose/testdata/OptionalPresent/pkg

@@ -1 +0,0 @@
-foo

internal/goose/testdata/StructOptionalField/foo/foo.go

@@ -1,23 +0,0 @@
-package main
-
-import "fmt"
-
-func main() {
-	fb := injectFooBar()
-	fmt.Println(fb.Foo, fb.OptionalBar)
-}
-
-type Foo int
-type Bar int
-
-//goose:provide Set
-//goose:optional OptionalBar
-type FooBar struct {
-	Foo         Foo
-	OptionalBar Bar
-}
-
-//goose:provide Set
-func provideFoo() Foo {
-	return 42
-}

internal/goose/testdata/StructOptionalField/foo/goose.go

@@ -1,7 +0,0 @@
-//+build gooseinject
-
-package main
-
-//goose:use Set
-
-func injectFooBar() FooBar

internal/goose/testdata/StructOptionalField/out.txt

@@ -1 +0,0 @@
-42 0

internal/goose/testdata/StructOptionalField/pkg

@@ -1 +0,0 @@
-foo

internal/goose/testdata/StructOptionalFieldPresent/foo/foo.go

@@ -1,28 +0,0 @@
-package main
-
-import "fmt"
-
-func main() {
-	fb := injectFooBar()
-	fmt.Println(fb.Foo, fb.Bar)
-}
-
-type Foo int
-type Bar int
-
-//goose:provide Set
-//goose:optional Bar
-type FooBar struct {
-	Foo Foo
-	Bar Bar
-}
-
-//goose:provide Set
-func provideFoo() Foo {
-	return 41
-}
-
-//goose:provide Set
-func provideBar() Bar {
-	return 1
-}

internal/goose/testdata/StructOptionalFieldPresent/foo/goose.go

@@ -1,7 +0,0 @@
-//+build gooseinject
-
-package main
-
-//goose:use Set
-
-func injectFooBar() FooBar

internal/goose/testdata/StructOptionalFieldPresent/out.txt

@@ -1 +0,0 @@
-41 1

internal/goose/testdata/StructOptionalFieldPresent/pkg

@@ -1 +0,0 @@
-foo