[test] remove pointless block_hashes.append(...)

Summary: This line duplicated the block hashes, as they were already saved in that list using the list returned by `generatetoaddress`. It didn't  cause any issue because all the following tests looped over the 101 first indices of that list, so the duplicated values were just ignored.

Test Plan:
with chronik
`ninja check-functional`

Reviewers: #bitcoin_abc, roqqit

Reviewed By: roqqit

Differential Revision: https://reviews.bitcoinabc.org/D16517

test/functional/chronik_block.py

@@ -103,7 +103,6 @@ def run_test(self):
             expected_proto_blocks.append(expected_proto)
             assert_equal(proto_block, expected_proto)
             assert_equal(proto_block, chronik.block(block_hashes[i]).ok())
-            block_hashes.append(proto_block.block_info.hash)
 
         # Using -chronikreindex results in the same data
         self.restart_node(0, ["-chronik", "-chronikreindex"])