Update list in mbed_targets.md

Update list with content from comments.

Author: Amanda Butler

docs/reference/configuration/mbed_targets.md

@@ -129,9 +129,8 @@ When you use target inheritance, you may alter the values of `extra_labels` usin
 
 The list of _features_ enables software features on a platform. Like `extra_labels`, `features` makes the build system aware of additional directories it must scan for resources. Unlike `extra_labels`, the build system recognizes a fixed set of values in the `features` list. The build system recognizes the following features:
 
+- `BOOTLOADER`.
 - `BLE`.
-- `STORAGE`.
-- `LWIP`.
 - `CRYPTOCELL310`.
 
 The build system errors when you use features outside of this list.