wl12xx: Remove obsolete testmode NVS push command

The testmode NVS push command is no longer in use. In addition, it has
several implementation issues that prevent it from working correctly:

1. wl1271_tm_cmd_configure relies on wl->chip.id being set. However,
   since the device was not necessarily booted by the time the function
   is called, wl->chip.id will be initialized to 0.
2. The NVS file is fetched by calling request_firmware() before it is
   possible to push an NVS file.
3. The maximum allowed size of nl binary payloads is not sufficient for
   pushing NVS files.
4. Pushing 128x NVS files will always fail due to a bug in the
   validation code.
5. In case the pushed NVS file is found invalid, the mutex will be kept
   locked and the nvs member will become a dangling pointer.

Since this feature is not being used, remove it completely instead of
fixing it.

Signed-off-by: Ido Yariv <ido@wizery.com>
Acked-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>