Remove transclusions in lp_ticker.md

Remove transclusions from nonexistent pages to fix build.

Author: Amanda Butler

docs/reference/contributing/target/lp_ticker.md

@@ -2,8 +2,6 @@
 
 Implementing the low power ticker enables Mbed OS to perform power efficient timing operations that only request millisecond accuracy. You can use this API to schedule events, record elapsed time and drive the tickless OS scheduler.
 
-<span class="warnings">**Warning:** We are changing the low power ticker HAL API in an upcoming release of Mbed OS. This page documents code that exists on a feature branch of Mbed OS. You can find details on how it may affect you in the [implementing the low power ticker API](#implementing-the-low-power-ticker-api) section.</span>
-
 ### Assumptions
 
 #### Defined behavior
@@ -48,14 +46,10 @@ Hardware low power ticker capabilities.
 
 ### Implementing the low power ticker API
 
-We are working on the new HAL low power ticker API, which will replace the current version in an upcoming release of Mbed OS. You need to implement the low power ticker API in both variants. First, you need to implement the current API. You can find it on master branch:
+You can find the API and specification for the low power ticker API in the following header file:
 
 [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.8/mbed-os-api-doxy/lp__ticker__api_8h_source.html)
 
-To make sure your platform is ready for the upcoming changes, you need to implement the future API and submit it in a separate pull request against the `feature-hal-spec-ticker` branch. You can find the API and specification for the new low power ticker API in the following header file:
-
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.8/feature-hal-spec-ticker-doxy/group__hal__lp__ticker.html)
-
 To enable low power ticker support in Mbed OS, add the `LPTICKER` label in the `device_has` option of the target's section in the `targets.json` file.
 
 ### Testing
@@ -65,11 +59,3 @@ The Mbed OS HAL provides a set of conformance tests for the low power ticker. Yo
 ```
 mbed test -t <toolchain> -m <target> -n tests-mbed_hal-common_ticker*,tests-mbed_hal-lp_ticker*
 ```
-
-You can read more about the test cases:
-
- [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.8/feature-hal-spec-ticker-doxy/group__hal__lp__ticker.html)
-
- [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.8/feature-hal-spec-ticker-doxy/group__hal__ticker__tests.html)
-
- [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.8/feature-hal-spec-ticker-doxy/group__hal__lp__ticker__tests.html)