Remove stray doc references to valgrind.

docs/layout_tests_linux.md

 # Running layout tests on Linux
 
 1.  Build `blink_tests` (see [Linux-specific build instructions](https://chromium.googlesource.com/chromium/src/+/master/docs/linux_build_instructions.md))
 1.  Checkout the layout tests
     *   If you have an entry in your `.gclient` file that includes
         "LayoutTests", you may need to comment it out and sync.
     *   You can run a subset of the tests by passing in a path relative to
         `src/third_party/WebKit/LayoutTests/`.  For example,
         `run_layout_tests.py fast` will only run the tests under
         `src/third_party/WebKit/LayoutTests/fast/`.
@@ skipping 22 matching lines @@
 You can also just run `build/install-build-deps.sh` again.
 
 ## Plugins
 
 If `fast/dom/object-plugin-hides-properties.html` and
 `plugins/embed-attributes-style.html` are failing, try uninstalling
 `totem-mozilla` from your system:
 
     sudo apt-get remove totem-mozilla
 
-
-## Running layout tests under valgrind on Linux
-
-As above, but use `tools/valgrind/chrome_tests.sh -t webkit` instead.  e.g.
-
-    sh tools/valgrind/chrome_tests.sh -t webkit LayoutTests/fast/
-
-This defaults to using --debug.  Read the script for more details.
-
-If you're trying to reproduce a run from the valgrind buildbot, look for the
-`--run_chunk=XX:YY` line in the bot's log. You can rerun exactly as the bot did
-with the commands.
-
-```shell
-cd ~/chromium/src
-echo XX > valgrind_layout_chunk.txt
-sh tools/valgrind/chrome_tests.sh -t layout -n YY
-```
-
-That will run the XXth chunk of YY layout tests.
-
 ## Configuration tips
 
 *   Use an optimized `content_shell` when rebaselining or running a lot of
     tests. ([bug 8475](https://crbug.com/8475) is about how the debug output
     differs from the optimized output.)
 
     `ninja -C out/Release content_shell`
 
 *   Make sure you have wdiff installed: `sudo apt-get install wdiff` to get
     prettier diff output.
@@ skipping 54 matching lines @@
 In your `.xmonad/xmonad.hs`, change your config to include a manageHook along
 these lines:
 
 ```
 test_shell_manage = className =? "Test_shell" --> doFloat
 main = xmonad $
   defaultConfig
     { manageHook = test_shell_manage <+> manageHook defaultConfig
     ...
 ```