Remove transclusions in QuadSPI.md

Remove transclusions from nonexistent pages to fix build.

Author: Amanda Butler

docs/reference/contributing/target/QuadSPI.md

@@ -4,8 +4,6 @@ Implementing QSPI enables Mbed OS to communicate with external memories much fas
 
 The most common use case is an external memory to use as additional data storage.
 
-<span class="warnings">**Warning:** We are changing the QSPI 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 QuadSPI](#implementing-quadspi) section.</span>
-
 ### Assumptions
 
 #### Defined behavior
@@ -23,10 +21,6 @@ QSPI peripheral
 
 ### Implementing QuadSPI
 
-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. You can find the API and specification for the new QuadSPI 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-qspi-doxy/classmbed_1_1_q_s_p_i.html)
-
 The target needs to define the `qspi_s` structure - target specific QSPI object.
 
 Functions to implement: