internal/syscall/unix: simplify KernelVersion

Since values[2] elements are initialized with 0, the switch statement
doesn't do anything. Remove it.

Change-Id: I41176692cdf0c01fe8e85315f0c0dc8b0f3d41fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/427675
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/internal/syscall/unix/kernel_version_linux.go

@@ -37,13 +37,6 @@ func KernelVersion() (major int, minor int) {
 			value = 0
 		}
 	}
-	switch vi {
-	case 0:
-		return 0, 0
-	case 1:
-		return values[0], 0
-	case 2:
-		return values[0], values[1]
-	}
-	return
+
+	return values[0], values[1]
 }