Replace CBlockHeader::GetHash with call to SerializeHash

Removes variability between LE and BE.
As suggested by @sipa.

src/primitives/block.cpp

@@ -12,18 +12,7 @@
 
 uint256 CBlockHeader::GetHash() const
 {
-#if defined(WORDS_BIGENDIAN)
-    uint8_t data[80];
-    WriteLE32(&data[0], nVersion);
-    memcpy(&data[4], hashPrevBlock.begin(), hashPrevBlock.size());
-    memcpy(&data[36], hashMerkleRoot.begin(), hashMerkleRoot.size());
-    WriteLE32(&data[68], nTime);
-    WriteLE32(&data[72], nBits);
-    WriteLE32(&data[76], nNonce);
-    return Hash(data, data + 80);
-#else // Can take shortcut for little endian
-    return Hash(BEGIN(nVersion), END(nNonce));
-#endif
+    return SerializeHash(*this);
 }
 
 uint256 CBlock::BuildMerkleTree(bool* fMutated) const