Don't rename main thread at process level

Summary:

Set only the internal name.

Fixes #17036 for both `bitcoind` and `bitcoin-qt`.

This fixes Unix tools like ps or pkill that use the process name
(called bitcoin-init since D5540).

Backport of core PR17038.

Depends on D5540.

Test Plan:

ninja check

bitcoind -daemon
ps -A | grep bitcoind # should return our bitcoind instance
sudo killall bitcoind
ps -A | grep bitcoind # should return nothing, kill successful

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D5544