syscall: use unsafe.Slice instead of unsafeheader package

Change-Id: I9de5aafb36d05bdc90bbdba516367eb2b200a7e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/428777
Auto-Submit: Tobias Klauser <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: tklauser

src/syscall/syscall_unix.go

@@ -11,7 +11,6 @@ import (
 	"internal/itoa"
 	"internal/oserror"
 	"internal/race"
-	"internal/unsafeheader"
 	"runtime"
 	"sync"
 	"unsafe"
@@ -57,11 +56,7 @@ func (m *mmapper) Mmap(fd int, offset int64, length int, prot int, flags int) (d
 	}
 
 	// Use unsafe to turn addr into a []byte.
-	var b []byte
-	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&b))
-	hdr.Data = unsafe.Pointer(addr)
-	hdr.Cap = length
-	hdr.Len = length
+	b := unsafe.Slice((*byte)(unsafe.Pointer(addr)), length)
 
 	// Register mapping in m and return it.
 	p := &b[cap(b)-1]

src/syscall/syscall_windows.go

@@ -12,7 +12,6 @@ import (
 	"internal/itoa"
 	"internal/oserror"
 	"internal/race"
-	"internal/unsafeheader"
 	"runtime"
 	"sync"
 	"unicode/utf16"
@@ -78,11 +77,7 @@ func utf16PtrToString(p *uint16) string {
 		n++
 	}
 	// Turn *uint16 into []uint16.
-	var s []uint16
-	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&s))
-	hdr.Data = unsafe.Pointer(p)
-	hdr.Cap = n
-	hdr.Len = n
+	s := unsafe.Slice((*uint16)(unsafe.Pointer(p)), n)
 	// Decode []uint16 into string.
 	return string(utf16.Decode(s))
 }