update linux instructions to not update clang

docs/getting_started.md

 # Getting Started
 
 How to get and build the libyuv code.
 
 ## Pre-requisites
 
 You'll need to have depot tools installed: https://www.chromium.org/developers/how-tos/install-depot-tools
 Refer to chromium instructions for each platform for other prerequisites.
 
 ## Getting the Code
@@ skipping 28 matching lines @@
 
     solutions = [
       { "name"        : "libyuv",
         "url"         : "https://chromium.googlesource.com/libyuv/libyuv",
         "deps_file"   : "DEPS",
         "managed"     : True,
         "custom_deps" : {
         },
         "safesync_url": "",
       },
-    ]
-    target_os = ["android", "unix"]
+    ];
+    target_os = ["android", "unix"];
 
 Then run:
 
     export GYP_DEFINES="OS=android"
     gclient sync
 
 For Windows the gclient sync must be done from an Administrator command prompt.
 
 The sync will generate native build files for your environment using gyp (Windows: Visual Studio, OSX: XCode, Linux: make). This generation can also be forced manually: `gclient runhooks`
 
@@ skipping 114 matching lines @@
 
 #### Building with GN
 
     call gn gen out/Release "--args=is_debug=false target_cpu=\"x86\""
     call gn gen out/Debug "--args=is_debug=true target_cpu=\"x86\""
     ninja -C out/Release
     ninja -C out/Debug
 
 ### Linux
 
-    tools/clang/scripts/update.sh
     GYP_DEFINES="target_arch=x64" ./gyp_libyuv
     ninja -j7 -C out/Debug
     ninja -j7 -C out/Release
 
     GYP_DEFINES="target_arch=ia32" ./gyp_libyuv
     ninja -j7 -C out/Debug
     ninja -j7 -C out/Release
 
 #### CentOS
 
@@ skipping 211 matching lines @@
     git checkout -b mycl -t origin/master
     git pull
     <edit files>
     git add -u
     git commit -m "my change"
     git cl lint
     git cl try
     git cl upload -r a-reviewer@chomium.org -s
     <once approved..>
     git cl land