docs: remove mentions of Kerberos dependency

The driver does not support Kerberos authentication anymore, so the
documentation has been updated to remove references to Kerberos and its
installation instructions.

Author: wprzytula

README.md

@@ -395,7 +395,7 @@ Some tests are added to GitHub Actions workflows and are used to test every pull
 
 To build and run the integration tests several requirements need to be met:
 
-* Install `libuv`, `openssl` and `kerberos` on your system:
+* Install `libuv` and `openssl` on your system:
 
 ```shell
 # On Ubuntu

docs/source/topics/building.md

@@ -22,17 +22,11 @@ The C/C++ driver depends on the following software:
 * [CMake] v2.6.4+
 * [libuv] 1.x
 * [OpenSSL] v1.0.x or v1.1.x \*
-* Kerberos v5 ([Heimdal] or [MIT]) \*\*\*
 
 __\*__ Use the `CASS_USE_OPENSSL` CMake option to enable/disable OpenSSL
          support. Disabling this option will disable SSL/TLS protocol support
          within the driver; defaults to `On`.
 
-__\*\*\*__ Use the `CASS_USE_KERBEROS` CMake option to enable/disable Kerberos
-       support. Enabling this option will enable Kerberos authentication
-       protocol within the driver (currently unusupported by Scylla);
-       defaults to `Off`.
-
 ## Linux/Mac OS
 
 The driver is known to build on CentOS/RHEL 6/7/8, Mac OS X 10.10/10.11 (Yosemite
@@ -71,20 +65,6 @@ brew upgrade
 brew install autoconf automake cmake libtool
 ```
 
-#### Kerberos
-
-##### CentOS/RHEL (Yum)
-
-```bash
-yum install krb5-devel
-```
-
-##### Ubuntu (APT)
-
-```bash
-apt-get install libkrb5-dev
-```
-
 #### libuv
 
 libuv v1.x should be used in order to ensure all features of the C/C++ driver
@@ -225,9 +205,5 @@ cmake -DCASS_BUILD_UNIT_TESTS=On ..
 [cpp-driver-ubuntu18-04]: https://github.com/scylladb/cpp-driver/releases/download/2.15.2-1/scylla-cpp-driver_2.15.2-1_amd64.deb
 [Homebrew]: https://brew.sh
 [CMake]: http://www.cmake.org/download
-[k4w-32]: http://web.mit.edu/kerberos/dist/kfw/4.0/kfw-4.0.1-i386.msi
-[k4w-64]: http://web.mit.edu/kerberos/dist/kfw/4.0/kfw-4.0.1-amd64.msi
 [libuv]: http://libuv.org
-[Heimdal]: https://www.h5l.org
-[MIT]: https://web.mit.edu/kerberos
 [OpenSSL]: https://www.openssl.org