Update installation.rst

1. the list of operation systems is outdated
2. not on any installation page we have the list of supported OSes
3. we have supported OSes in our lifecycle doc - why add it here?

docs/installation.rst

@@ -4,21 +4,6 @@
 Installing Percona Toolkit
 ==========================
 
-Percona provides packages for most popular 64-bit Linux distributions:
-
-* Debian 7 ("wheezy")
-* Debian 8 ("jessie")
-* Ubuntu 14.04 LTS (Trusty Tahr)
-* Ubuntu 16.04 LTS (Xenial Xerus)
-* Ubuntu 16.10 (Yakkety Yak)
-* Ubuntu 17.04 (Zesty Zapus)
-* Red Hat Enterprise Linux or CentOS 6 (Santiago)
-* Red Hat Enterprise Linux or CentOS 7 (Maipo)
-
-.. note:: Percona Toolkit should work on other DEB-based and RPM-based systems
-   (for example, Oracle Linux and Amazon Linux AMI),
-   but it is tested only on those listed above.
-
 It is recommended to install Percona software from official repositories:
 
 1. Configure Percona repositories as described in