Merge bitcoin/bitcoin#23469: doc: Remove Boost build note from build-unix.md

ea360d6 doc: remove redundant optionals from build-unix.md (fanquake)
b971858 doc: remove Boost build note from build-unix.md (fanquake)

Pull request description:

  We don't have build instructions for any other dependency, and in any case, this isn't something we should maintain in our docs. If someone wants to know how to build Boost, or any other dependency, they can look at the relevant website / external build documentation.

ACKs for top commit:
  jarolrod:
    ACK ea360d6

Tree-SHA512: c7389b5f051f79c728d8ea0725143affeb2c35b1e3c20d5cd441c6ac540d230698c47bf2c57feb12e7b6bffd2f337c1c83a9cd3a928ce5c479cdbbdf8f61fba4

Author: MarcoFalke

doc/build-unix.md

@@ -42,12 +42,12 @@ Optional dependencies:
  ------------|------------------|----------------------
  miniupnpc   | UPnP Support     | Firewall-jumping support
  libnatpmp   | NAT-PMP Support  | Firewall-jumping support
- libdb4.8    | Berkeley DB      | Optional, wallet storage (only needed when legacy wallet enabled)
+ libdb4.8    | Berkeley DB      | Wallet storage (only needed when legacy wallet enabled)
  qt          | GUI              | GUI toolkit (only needed when GUI enabled)
- libqrencode | QR codes in GUI  | Optional for generating QR codes (only needed when GUI enabled)
- libzmq3     | ZMQ notification | Optional, allows generating ZMQ notifications (requires ZMQ version >= 4.0.0)
- sqlite3     | SQLite DB        | Optional, wallet storage (only needed when descriptor wallet enabled)
- systemtap   | Tracing (USDT)   | Optional, statically defined tracepoints
+ libqrencode | QR codes in GUI  | QR code generation (only needed when GUI enabled)
+ libzmq3     | ZMQ notification | ZMQ notifications (requires ZMQ version >= 4.0.0)
+ sqlite3     | SQLite DB        | Wallet storage (only needed when descriptor wallet enabled)
+ systemtap   | Tracing (USDT)   | Statically defined tracepoints
 
 For the versions used, see [dependencies.md](dependencies.md)
 
@@ -234,15 +234,6 @@ Otherwise, you can build Bitcoin Core from self-compiled [depends](/depends/READ
 
 **Note**: You only need Berkeley DB if the wallet is enabled (see [*Disable-wallet mode*](#disable-wallet-mode)).
 
-Boost
------
-If you need to build Boost yourself:
-
-    sudo su
-    ./bootstrap.sh
-    ./bjam install
-
-
 Security
 --------
 To help make your Bitcoin Core installation more secure by making certain attacks impossible to