doc: Remove cros_workon_make

Change-Id: I94a1b35e9680eb369382f83e69672fcb1a2eb19b
diff --git a/docs/custom_vm.md b/docs/custom_vm.md
index 57a1b0d..5e2d933 100644
--- a/docs/custom_vm.md
+++ b/docs/custom_vm.md
@@ -89,7 +89,6 @@
 (cr) cros workon -b ferrochrome start \
 chromeos-base/chromeos-chrome \
 chromeos-base/chrome-icu
-(cr) cros_workon_make --board ferrochrome chromeos-chrome
 ```
 
 Optionally, if you have touched the kernel source code (which is under