doc: remove dependency install instructions from win docs

This duplicates what is in depends, and is outdated.

depends/README.md

@@ -54,7 +54,7 @@ For more information, see [SDK Extraction](../contrib/macdeploy/README.md#sdk-ex
 
 #### For Win64 cross compilation
 
-- see [build-windows.md](../doc/build-windows.md#cross-compilation-for-ubuntu-and-windows-subsystem-for-linux)
+    apt install g++-mingw-w64-x86-64-posix
 
 #### For linux (including i386, ARM) cross compilation
 

doc/build-windows.md

@@ -28,36 +28,18 @@ The steps below can be performed on Ubuntu or WSL. The depends system
 will also work on other Linux distributions, however the commands for
 installing the toolchain will be different.
 
-First, install the general dependencies:
-
-    sudo apt update
-    sudo apt upgrade
-    sudo apt install cmake curl g++ git make pkg-config
-
-A host toolchain (`g++`) is necessary because some dependency
-packages need to build host utilities that are used in the build process.
-
-See [dependencies.md](dependencies.md) for a complete overview.
+See [README.md](../depends/README.md) in the depends directory for which
+dependencies to install and [dependencies.md](dependencies.md) for a complete overview.
 
 If you want to build the Windows installer using the `deploy` build target, you will need [NSIS](https://nsis.sourceforge.io/Main_Page):
 
-    sudo apt install nsis
+    apt install nsis
 
 Acquire the source in the usual way:
 
     git clone https://github.com/bitcoin/bitcoin.git
     cd bitcoin
 
-## Building for 64-bit Windows
-
-The first step is to install the mingw-w64 cross-compilation toolchain:
-
-```sh
-sudo apt install g++-mingw-w64-x86-64-posix
-```
-
-Once the toolchain is installed the build steps are common:
-
 Note that for WSL the Bitcoin Core source path MUST be somewhere in the default mount file system, for
 example /usr/src/bitcoin, AND not under /mnt/d/. If this is not the case the dependency autoconf scripts will fail.
 This means you cannot use a directory that is located directly on the host Windows file system to perform the build.