Remove stray doc references to valgrind.

docs/linux_debugging.md

 # Tips for debugging on Linux
 
 This page is for Chromium-specific debugging tips; learning how to run gdb is
 out of scope.
 
 [TOC]
 
 ## Symbolized stack trace
 
 The sandbox can interfere with the internal symbolizer. Use `--no-sandbox` (but
@@ skipping 393 matching lines @@
 
 or within gdb:
 
     set environment CHROME_IPC_LOGGING 1
 
 If some messages show as unknown, check if the list of IPC message headers in
 [chrome/common/logging_chrome.cc](/chrome/common/logging_chrome.cc) is
 up to date. In case this file reference goes out of date, try looking for usage
 of macros like `IPC_MESSAGE_LOG_ENABLED` or `IPC_MESSAGE_MACROS_LOG_ENABLED`.
 
-## Using valgrind
-
-To run valgrind on the browser and renderer processes, with our suppression file
-and flags:
-
-    $ cd $CHROMIUM_ROOT/src
-    $ tools/valgrind/valgrind.sh out/Debug/chrome
-
-You can use valgrind on chrome and/or on the renderers e.g
-`valgrind --smc-check=all ../sconsbuild/Debug/chrome`
-or by passing valgrind as the argument to `--render-cmd-prefix`.
-
-Beware that there are several valgrind "false positives" e.g. pickle, sqlite and
-some instances in webkit that are ignorable. On systems with prelink and address
-space randomization (e.g. Fedora), you may also see valgrind errors in libstdc++
-on startup and in gnome-breakpad.
-
-Valgrind doesn't seem to play nice with tcmalloc. To disable tcmalloc set the GN arg:
-
-    use_allocator="none"
-
-and rebuild.
-
 ## Profiling
 
 See
 https://sites.google.com/a/chromium.org/dev/developers/profiling-chromium-and-webkit
 and [Linux Profiling](linux_profiling.md).
 
 ## i18n
 
 We obey your system locale. Try something like:
 
@@ skipping 90 matching lines @@
 [Running layout tests on Linux](layout_tests_linux.md) page.
 
 If you need to test something with hardware accelerated compositing
 (e.g., compiz), you can use `Xgl` (`sudo apt-get install xserver-xgl`). E.g.:
 
     Xgl :1 -ac -accel glx:pbuffer -accel xv:pbuffer -screen 1024x768
 
 ## Mozilla Tips
 
 https://developer.mozilla.org/en/Debugging_Mozilla_on_Linux_FAQ