Remove references to DrMemory from chromium repo.

This removes references to DrMemory for MB, GN and buildbot, and also
removes references to redundant DrMemory bots and DrMemory targets.

BUG=655521, 644217

Review-Url: https://codereview.chromium.org/2455463002
Cr-Original-Commit-Position: refs/heads/master@{#430388}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e02ee8681a05a4e85552ec37e2a6999b0f2e76d9
diff --git a/tools/gn/docs/cookbook.md b/tools/gn/docs/cookbook.md
index 66a44f7..0f3d101 100644
--- a/tools/gn/docs/cookbook.md
+++ b/tools/gn/docs/cookbook.md
@@ -204,7 +204,6 @@
 | `arm_version`                                   | `arm_version`                              | `//build/config/arm.gni`                       |
 | `asan` (0/1)                                    | `is_asan` (true/false)                     | `//build/config/sanitizers/sanitizers.gni`     |
 | `branding` ("Chromium"/"Chrome")                | `is_chrome_branded` (true/false)           | `//build/config/chrome_build.gni`              |
-| `build_for_tool=="drmemory"`                    | `enable_iterator_debugging=false`          | (internal to `//build/config/BUILD.gn`)        |
 | `build_for_tool=="tsan"`                        | `enable_iterator_debugging=false`          | (internal to `//build/config/BUILD.gn`)        |
 | `buildtype` ("Official"/"Dev")                  | `is_official_build` (true/false)           | `//build/config/chrome_build.gni`              |
 | `chrome_multiple_dll` (0/1)                     | `is_multi_dll_chrome` (true/false)         | `//build/config/chrome_build.gni`              |