build: remove need to test for endianness

We can cherry-pick one commit from upstream leveldb, make the same change in crc32c, and then ultimately drop our build infra for testing endianness.

Not for merging until subtrees are updated:

• https://github.com/bitcoin-core/crc32c-subtree/pull/7
• https://github.com/bitcoin-core/leveldb-subtree/pull/40 - Done in https://github.com/bitcoin/bitcoin/pull/31671.