crypto/aes: remove redundant nil check around loop

Change-Id: I8cc4b5efe798e74b6daabd64fc2dd5486dcb7c5e
GitHub-Last-Rev: 694509e33df7c5729ec0bf7b053ff18ebd87c36b
GitHub-Pull-Request: golang/go#28115
Reviewed-on: https://go-review.googlesource.com/c/140998
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/crypto/aes/aes_test.go

@@ -231,7 +231,6 @@ L:
 				continue L
 			}
 		}
-		if dec != nil {
 		for j, v := range dec {
 			if v != tt.dec[j] {
 				t.Errorf("key %d: dec[%d] = %#x, want %#x", i, j, v, tt.dec[j])
@@ -239,7 +238,6 @@ L:
 			}
 		}
 	}
-	}
 }
 
 // Appendix B, C of FIPS 197: Cipher examples, Example vectors.