Documentation: Remove references to optional BouncyCastle libraries

BouncyCastle is bundled with Gerrit since 2.14:
https://www.gerritcodereview.com/releases/2.14.md#Bouncy-Castle-Libraries

Documentation/install-j2ee.txt still needs an update to this.

Change-Id: I461d5d5f7da5bd25f99941fcc525113d5ac09bea

Documentation/install.txt

diff --git a/Documentation/install.txt b/Documentation/install.txt
index f0a1730..2adc343 100644
--- a/Documentation/install.txt
+++ b/Documentation/install.txt
@@ -175,8 +175,8 @@
 [[installation_on_windows]]
 == Installation on Windows
 
-If new site is going to be initialized with Bouncy Castle cryptography,
-ssh-keygen command must be available during the init phase. If you have
+The `ssh-keygen` command must be available during the init phase to
+generate SSH host keys. If you have
 link:https://git-for-windows.github.io/[Git for Windows] installed,
 start Command Prompt and temporary add directory with ssh-keygen to the
 PATH environment variable just before running init command: