Remove transclusions from rtc.md

Remove transclusions from nonexistent pages to fix build.

Author: Amanda Butler

docs/reference/contributing/target/rtc.md

@@ -2,8 +2,6 @@
 
 Implementing RTC enables Mbed OS to keep track of the current time. The standard library time keeping functions, such as `time`, use it.
 
-<span class="warnings">**Warning:** We are changing the RTC 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 RTC API](#implementing-the-rtc-api) section.</span>
-
 ### Assumptions
 
 #### Defined behavior
@@ -32,14 +30,10 @@ Hardware RTC capabilities.
 
 ### Implementing the RTC API
 
-We are working on the new HAL RTC API, which will replace the current version in an upcoming release of Mbed OS. You need to implement the RTC API in both variants. First, you need to implement the current API. You can find it on the master branch:
+You can find the API and specification for the RTC 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/rtc__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-rtc` branch. You can find the API and specification for the new RTC 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-rtc-doxy/group__hal__rtc.html)
-
 To enable RTC support in Mbed OS, add the `RTC` label in the `device_has` option of the target's section in the `targets.json` file.
 
 ### Testing
@@ -49,7 +43,3 @@ The Mbed OS HAL provides a set of conformance tests for RTC. You can use these t
 ```
 mbed test -t <toolchain> -m <target> -n "tests-mbed_hal-rtc*"
 ```
-
-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-rtc-doxy/group__hal__rtc__tests.html)