Revert "Merge #16367: Multiprocess build support"

This reverts the changes made in merge commit
1b30761360:

This reverts commit b919efadff.
This reverts commit d54f64c6c7.
This reverts commit 787f40668d.
This reverts commit d630646662.
This reverts commit e6e44eedd5.

.gitignore

@@ -5,8 +5,6 @@
 src/bitcoin
 src/bitcoind
 src/bitcoin-cli
-src/bitcoin-gui
-src/bitcoin-node
 src/bitcoin-tx
 src/bitcoin-wallet
 src/test/fuzz