Update recommended Python version in the getting started sections (#1525)

* Update recommended Python version in the getting started section to 3.8
* Remove mentioning of old Python versions in linux.md
* Removing LTS deprecation note

Author: svekars

_get_started/installation/linux.md

@@ -40,8 +40,6 @@ If you decide to use APT, you can run the following command to install it:
 sudo apt install python
 ```
 
-> It is recommended that you use Python 3.6, 3.7 or 3.8, which can be installed via any of the mechanisms above .
-
 > If you use [Anaconda](#anaconda) to install PyTorch, it will install a sandboxed version of Python that will be used for running PyTorch applications.
 
 ### Package Manager

_includes/quick_start_local.html

@@ -5,6 +5,9 @@
   <a href="{{ site.baseurl }}/get-started/previous-versions">install previous versions of PyTorch</a>. Note that LibTorch is only available for C++.
 </p>
 
+<p><b>NOTE:</b> Latest PyTorch requires Python 3.8 or later.
+</p>
+
 <div class="row">
   <div class="col-md-3 headings">
     <div class="col-md-12 title-block">
@@ -109,6 +112,3 @@
   </div>
 </div>
 <br>
-<p><b>NOTE:</b> PyTorch LTS has been deprecated. For more information, see
-   <a href="{{ site.baseurl }}/blog/pytorch-enterprise-support-update/">this blog</a>.
-</p>