Update 12-interpolation.md (#19159)

Removed duplicate lines.

content/compose/compose-file/12-interpolation.md

@@ -63,63 +63,3 @@ services:
     labels:
       - "$VAR_INTERPOLATED_BY_COMPOSE=BAR"
 ```
-
-Values in a Compose file can be set by variables and interpolated at runtime. Compose files use a Bash-like
-syntax `${VARIABLE}`.
-
-Both `$VARIABLE` and `${VARIABLE}` syntax is supported. Default values can be defined inline using typical shell syntax:
-
-- `${VARIABLE:-default}` evaluates to `default` if `VARIABLE` is unset or
-  empty in the environment.
-- `${VARIABLE-default}` evaluates to `default` only if `VARIABLE` is unset
-  in the environment.
-
-Similarly, the following syntax allows you to specify mandatory variables:
-
-- `${VARIABLE:?err}` exits with an error message containing `err` if
-  `VARIABLE` is unset or empty in the environment.
-- `${VARIABLE?err}` exits with an error message containing `err` only if
-  `VARIABLE` is unset in the environment.
-
-Interpolation can also be nested:
-
-- `${VARIABLE:-${FOO}}`
-- `${VARIABLE?$FOO}`
-- `${VARIABLE:-${FOO:-default}}`
-
-Other extended shell-style features, such as `${VARIABLE/foo/bar}`, are not
-supported by Compose.
-
-You can use a `$$` (double-dollar sign) when your configuration needs a literal
-dollar sign. This also prevents Compose from interpolating a value, so a `$$`
-allows you to refer to environment variables that you don't want processed by
-Compose.
-
-```yml
-web:
-  build: .
-  command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
-```
-
-If Compose can't resolve a substituted variable and no default value is defined, it displays a warning and substitutes the variable with an empty string.
-
-As any values in a Compose file can be interpolated with variable substitution, including compact string notation
-for complex elements, interpolation is applied before a merge on a per-file basis.
-
-Interpolation applies only to YAML values, not to keys. For the few places where keys are actually arbitrary
-user-defined strings, such as [labels](05-services.md#labels) or [environment](05-services.md#environment), an alternate equal sign syntax
-must be used for interpolation to apply. For example:
-
-```yml
-services:
-  foo:
-    labels:
-      "$VAR_NOT_INTERPOLATED_BY_COMPOSE": "BAR"
-```
-
-```yml
-services:
-  foo:
-    labels:
-      - "$VAR_INTERPOLATED_BY_COMPOSE=BAR"
-```