acvp: drop 3DES fields from output when unused.

Change-Id: Ibc7f1b70deca0e1541c3f32271e57fc0320e6a05
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/45185
Reviewed-by: David Benjamin <davidben@google.com>

util/fipstools/acvp/acvptool/subprocess/block.go

diff --git a/util/fipstools/acvp/acvptool/subprocess/block.go b/util/fipstools/acvp/acvptool/subprocess/block.go
index 3765473..f0431be 100644
--- a/util/fipstools/acvp/acvptool/subprocess/block.go
+++ b/util/fipstools/acvp/acvptool/subprocess/block.go
@@ -282,9 +282,9 @@
 	IVHex         string `json:"iv,omitempty"`
 
 	// 3DES tests serialise the key differently.
-	Key1Hex string `json:"key1"`
-	Key2Hex string `json:"key2"`
-	Key3Hex string `json:"key3"`
+	Key1Hex string `json:"key1,omitempty"`
+	Key2Hex string `json:"key2,omitempty"`
+	Key3Hex string `json:"key3,omitempty"`
 }
 
 func (b *blockCipher) Process(vectorSet []byte, m Transactable) (interface{}, error) {