docs: device_link.rst: remove duplicated kernel-doc include

The infrastructure.rst file already includes the external
symbols from drivers/base/core.c.

Duplicating 3 functions there causes namespace collisions:

Documentation/driver-api/device_link.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/infrastructure'.
Declaration is 'device_link_state'.
Documentation/driver-api/device_link.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/infrastructure'.
Declaration is 'device_link_add'.
Documentation/driver-api/device_link.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/infrastructure'.
Declaration is 'device_link_del'.
Documentation/driver-api/device_link.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/infrastructure'.
Declaration is 'device_link_remove'.

So, drop the reference, adding just a mention to the functions
associated with device_link.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/driver-api/device_link.rst

···
 API
 ===
 
-.. kernel-doc:: drivers/base/core.c
-   :functions: device_link_add device_link_del device_link_remove
+See device_link_add(), device_link_del() and device_link_remove().