docs: remove protobuf from docs

Author: fanquake

doc/build-unix.md

@@ -44,7 +44,6 @@ Optional dependencies:
  miniupnpc   | UPnP Support     | Firewall-jumping support
  libdb4.8    | Berkeley DB      | Wallet storage (only needed when wallet enabled)
  qt          | GUI              | GUI toolkit (only needed when GUI enabled)
- protobuf    | Payments in GUI  | Data interchange format used for payment protocol (only needed when BIP70 enabled)
  libqrencode | QR codes in GUI  | Optional for generating QR codes (only needed when GUI enabled)
  univalue    | Utility          | JSON parsing and encoding (bundled version will be used unless --with-system-univalue passed to configure)
  libzmq3     | ZMQ notification | Optional, allows generating ZMQ notifications (requires ZMQ version >= 4.0.0)
@@ -118,10 +117,6 @@ libqrencode (optional) can be installed with:
 
     sudo apt-get install libqrencode-dev
 
-protobuf (optional) can be installed with:
-
-    sudo apt-get install libprotobuf-dev protobuf-compiler
-
 Once these are installed, they will be found by configure and a bitcoin-qt executable will be
 built by default.
 
@@ -150,10 +145,6 @@ libqrencode (optional) can be installed with:
 
     sudo dnf install qrencode-devel
 
-protobuf (optional) can be installed with:
-
-    sudo dnf install protobuf-devel
-
 Notes
 -----
 The release is built with GCC and then "strip bitcoind" to strip the debug

doc/build-windows.md

@@ -62,8 +62,7 @@ First, install the general dependencies:
     sudo apt install build-essential libtool autotools-dev automake pkg-config bsdmainutils curl git
 
 A host toolchain (`build-essential`) is necessary because some dependency
-packages (such as `protobuf`) need to build host utilities that are used in the
-build process.
+packages need to build host utilities that are used in the build process.
 
 See [dependencies.md](dependencies.md) for a complete overview.
 

doc/dependencies.md

@@ -19,7 +19,6 @@ These are the dependencies currently used by Bitcoin Core. You can find instruct
 | MiniUPnPc | [2.0.20180203](http://miniupnp.free.fr/files) |  | No |  |  |
 | OpenSSL | [1.0.1k](https://www.openssl.org/source) |  | Yes |  |  |
 | PCRE |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) |
-| protobuf | [2.6.1](https://github.com/google/protobuf/releases) |  | No |  |  |
 | Python (tests) |  | [3.5](https://www.python.org/downloads) |  |  |  |
 | qrencode | [3.4.4](https://fukuchi.org/works/qrencode) |  | No |  |  |
 | Qt | [5.9.7](https://download.qt.io/official_releases/qt/) | [5.5.1](https://github.com/bitcoin/bitcoin/issues/13478) | No |  |  |
@@ -35,7 +34,6 @@ Some dependencies are not needed in all configurations. The following are some f
 #### Options passed to `./configure`
 * MiniUPnPc is not needed with  `--with-miniupnpc=no`.
 * Berkeley DB is not needed with `--disable-wallet`.
-* protobuf is only needed with `--enable-bip70`.
 * Qt is not needed with `--without-gui`.
 * If the qrencode dependency is absent, QR support won't be added. To force an error when that happens, pass `--with-qrencode`.
 * ZeroMQ is needed only with the `--with-zmq` option.