Dev Docs: drop mention of endianness in hash byte order

[harding]

This tries to quickly solve some of the issues raised in #1061 and #1102 about the description of endianness in the hash byte order text.

In my opinion, simply thinking about hashes as having endianness tends to confuse developers, since hashes are usually treated as byte arrays rather than numbers. This PR simply drops the references to endianness in the hopes of minimizing confusion to new developers as well as allowing established developers to spend less time arguing about whether header hashes in Bitcoin are little or big endian.

I'm 100% open to a better patch that describes all the relevant considerations so far discussed, although I think it might be better to put that on the Wiki and then link to it from here. (That's a suggestion; feel free to PR it here if you think it's important.)

Screenshot of the revised section:

[harding]

@mruddy cherry-picked and adjusted your commit https://github.com/mruddy/bitcoin.org/commit/9f1885beae3e1f32b2072be2501fb5d6154ee3d8 to this PR. Please let me know if that looks ok.

Current rendered section:

[mruddy]

LGTM.
I'll go close my PR #1102.

[harding]

@mruddy thanks!

In the absence of critical feedback, this PR will we merged on Friday.