Remove deprecated Stack() []uintptr interface (#45)

* Remove deprecated Stack() []uintptr interface

* move TestStack to TestStacktrace
diff --git a/errors_test.go b/errors_test.go
index d3780f1..30796d8 100644
--- a/errors_test.go
+++ b/errors_test.go
@@ -197,61 +197,6 @@
 	}
 }
 
-func TestStack(t *testing.T) {
-	type fileline struct {
-		file string
-		line int
-	}
-	tests := []struct {
-		err  error
-		want []fileline
-	}{{
-		New("ooh"), []fileline{
-			{"github.com/pkg/errors/errors_test.go", 209},
-		},
-	}, {
-		Wrap(New("ooh"), "ahh"), []fileline{
-			{"github.com/pkg/errors/errors_test.go", 213}, // this is the stack of Wrap, not New
-		},
-	}, {
-		Cause(Wrap(New("ooh"), "ahh")), []fileline{
-			{"github.com/pkg/errors/errors_test.go", 217}, // this is the stack of New
-		},
-	}, {
-		func() error { return New("ooh") }(), []fileline{
-			{"github.com/pkg/errors/errors_test.go", 221}, // this is the stack of New
-			{"github.com/pkg/errors/errors_test.go", 221}, // this is the stack of New's caller
-		},
-	}, {
-		Cause(func() error {
-			return func() error {
-				return Errorf("hello %s", fmt.Sprintf("world"))
-			}()
-		}()), []fileline{
-			{"github.com/pkg/errors/errors_test.go", 228}, // this is the stack of Errorf
-			{"github.com/pkg/errors/errors_test.go", 229}, // this is the stack of Errorf's caller
-			{"github.com/pkg/errors/errors_test.go", 230}, // this is the stack of Errorf's caller's caller
-		},
-	}}
-	for _, tt := range tests {
-		x, ok := tt.err.(interface {
-			Stack() []uintptr
-		})
-		if !ok {
-			t.Errorf("expected %#v to implement Stack()", tt.err)
-			continue
-		}
-		st := x.Stack()
-		for i, want := range tt.want {
-			frame := Frame(st[i])
-			file, line := fmt.Sprintf("%+s", frame), frame.line()
-			if file != want.file || line != want.line {
-				t.Errorf("frame %d: expected %s:%d, got %s:%d", i, want.file, want.line, file, line)
-			}
-		}
-	}
-}
-
 // errors.New, etc values are not expected to be compared by value
 // but the change in errors#27 made them incomparable. Assert that
 // various kinds of errors have a functional equality operator, even
diff --git a/stack.go b/stack.go
index 882e051..4794a2f 100644
--- a/stack.go
+++ b/stack.go
@@ -79,9 +79,6 @@
 // stack represents a stack of program counters.
 type stack []uintptr
 
-// Deprecated: use Stacktrace()
-func (s *stack) Stack() []uintptr { return *s }
-
 func (s *stack) Stacktrace() []Frame {
 	f := make([]Frame, len(*s))
 	for i := 0; i < len(f); i++ {
diff --git a/stack_test.go b/stack_test.go
index 36dbe6d..1272c95 100644
--- a/stack_test.go
+++ b/stack_test.go
@@ -168,3 +168,58 @@
 		}
 	}
 }
+
+func TestStacktrace(t *testing.T) {
+	type fileline struct {
+		file string
+		line int
+	}
+	tests := []struct {
+		err  error
+		want []fileline
+	}{{
+		New("ooh"), []fileline{
+			{"github.com/pkg/errors/stack_test.go", 181},
+		},
+	}, {
+		Wrap(New("ooh"), "ahh"), []fileline{
+			{"github.com/pkg/errors/stack_test.go", 185}, // this is the stack of Wrap, not New
+		},
+	}, {
+		Cause(Wrap(New("ooh"), "ahh")), []fileline{
+			{"github.com/pkg/errors/stack_test.go", 189}, // this is the stack of New
+		},
+	}, {
+		func() error { return New("ooh") }(), []fileline{
+			{"github.com/pkg/errors/stack_test.go", 193}, // this is the stack of New
+			{"github.com/pkg/errors/stack_test.go", 193}, // this is the stack of New's caller
+		},
+	}, {
+		Cause(func() error {
+			return func() error {
+				return Errorf("hello %s", fmt.Sprintf("world"))
+			}()
+		}()), []fileline{
+			{"github.com/pkg/errors/stack_test.go", 200}, // this is the stack of Errorf
+			{"github.com/pkg/errors/stack_test.go", 201}, // this is the stack of Errorf's caller
+			{"github.com/pkg/errors/stack_test.go", 202}, // this is the stack of Errorf's caller's caller
+		},
+	}}
+	for _, tt := range tests {
+		x, ok := tt.err.(interface {
+			Stacktrace() []Frame
+		})
+		if !ok {
+			t.Errorf("expected %#v to implement Stacktrace() []Frame", tt.err)
+			continue
+		}
+		st := x.Stacktrace()
+		for i, want := range tt.want {
+			frame := st[i]
+			file, line := fmt.Sprintf("%+s", frame), frame.line()
+			if file != want.file || line != want.line {
+				t.Errorf("frame %d: expected %s:%d, got %s:%d", i, want.file, want.line, file, line)
+			}
+		}
+	}
+}