Replace Entropy with RAND_bytes

/dev/urandom is not an approved random number generator
for NIAP certification. Changing to use BoringSSL's
RAND_bytes(), which is approved.

Bug: 121272336
Test: Ran Keystore CTS tests against Walleye, no new
      test failures observed.
Change-Id: I0fb87c955512074fa714c1986ce99063ab430470
Merged-In: I579d140ef56c90b477b0d8989e3b02375681aee8
diff --git a/keystore/blob.h b/keystore/blob.h
index 665e07a..6a52ca4 100644
--- a/keystore/blob.h
+++ b/keystore/blob.h
@@ -82,7 +82,6 @@
     TYPE_KEY_CHARACTERISTICS = 5,
 } BlobType;
 
-class Entropy;
 
 class Blob {
   public:
@@ -121,8 +120,7 @@
     keystore::SecurityLevel getSecurityLevel() const;
     void setSecurityLevel(keystore::SecurityLevel);
 
-    ResponseCode writeBlob(const std::string& filename, const uint8_t* aes_key, State state,
-                           Entropy* entropy);
+    ResponseCode writeBlob(const std::string& filename, const uint8_t* aes_key, State state);
     ResponseCode readBlob(const std::string& filename, const uint8_t* aes_key, State state);
 
   private: