Revert "Update the cmd entry of the dvc.yaml file to add cmd as list …

…option (#1980)"

This reverts commit 23247d8.

content/docs/command-reference/repro.md

@@ -48,10 +48,6 @@ commands (`cmd` field of `dvc.yaml`). [Stage](/doc/command-reference/run)
 outputs are deleted from the <abbr>workspace</abbr> before executing the stage
 commands that produce them (unless `persist: true` is used in `dvc.yaml`).
 
-For stages with multiple commands (having a list in the `cmd` field), commands
-are run one after the other in the order they are defined. The failure of any
-command will halt the remaining stage execution, and raises an error.
-
 There are a few ways to restrict what will be regenerated by this command: by
 specifying specific reproduction [`targets`](#options), or by using certain
 command [options](#options), such as `--single-item` or `--all-pipelines`.
@@ -185,7 +181,7 @@ up-to-date and only execute the final stage.
 
 - `-q`, `--quiet` - do not write anything to standard output. Exit with 0 if all
   stages are up to date or if all stages are successfully executed, otherwise
-  exit with 1. The commands defined in the stage are free to write output
+  exit with 1. The command defined in the stage is free to write output
   regardless of this flag.
 
 - `-v`, `--verbose` - displays detailed tracing information.
@@ -268,8 +264,8 @@ If we now run `dvc repro`, we should see this:
 ```dvc
 $ dvc repro
 Stage 'filter' didn't change, skipping
-Running stage 'count':
-> python process.py numbers.txt > count.txt
+Running stage 'count' with command:
+        python process.py numbers.txt > count.txt
 Updating lock file 'dvc.lock'
 ```
 
@@ -305,8 +301,8 @@ of only the target (`count`) and following stages (none in this case):
 
 ```dvc
 $ dvc repro --downstream count
-Running stage 'count':
-> python process.py numbers.txt > count.txt
+Running stage 'count' with command:
+        python process.py numbers.txt > count.txt
 Updating lock file 'dvc.lock'
 ```
 

content/docs/user-guide/dvc-files-and-directories.md

@@ -135,9 +135,7 @@ stages:
       - performance.json
   training:
     desc: Training stage description
-    cmd:
-      - pip install -r requirements.txt
-      - python train.py
+    cmd: python train.py
     deps:
       - train.py
       - features
@@ -156,10 +154,7 @@ stages:
 by the user with the `--name` (`-n`) option of `dvc run`. Each stage can contain
 the following fields:
 
-- `cmd` (always present): One or more commands executed by the stage (may
-  contain either a single value, or a list). Commands are executed sequentially
-  until all are finished or until one of them fails (see
-  [`dvc repro`](/doc/command-reference/repro) for details).
+- `cmd` (always present): Executable command defined in this stage
 - `wdir`: Working directory for the stage command to run in (relative to the
   file's location). If this field is not present explicitly, it defaults to `.`
   (the file's location).