syscall: delete unreachable code

Change-Id: Iacedb792c73591b7fd75e836aab8e0e117c8e738
Reviewed-on: https://go-review.googlesource.com/27494
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/dll_windows.go

@@ -176,7 +176,6 @@ func (p *Proc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {
 	default:
 		panic("Call " + p.Name + " with too many arguments " + itoa(len(a)) + ".")
 	}
-	return
 }
 
 // A LazyDLL implements access to a single DLL.

src/syscall/exec_plan9.go

@@ -298,11 +298,6 @@ childerror1:
 	for {
 		RawSyscall(SYS_EXITS, 0, 0, 0)
 	}
-
-	// Calling panic is not actually safe,
-	// but the for loop above won't break
-	// and this shuts up the compiler.
-	panic("unreached")
 }
 
 // close the numbered file descriptor, unless it is fd1, fd2, or a member of fds.

src/syscall/exec_windows.go

@@ -209,8 +209,6 @@ func joinExeDirAndFName(dir, p string) (name string, err error) {
 			return FullPath(d + "\\" + p)
 		}
 	}
-	// we shouldn't be here
-	return "", EINVAL
 }
 
 type ProcAttr struct {