Remove duplicate symlinks

Now that the copy-firmware.sh script can create symlinks from the Link:
entries in the WHENCE file on the fly, remove the duplicate symlinks
from the filesystem.

One odd entry was intel/dsp_fw_cnl.bin which was listed both as symlink
and as a regular file. Both entries can be removed since the it's really
a symlink, so it will be recreated at installation time.

While at it, update the check_whence.py script to not look for the
existence of symlinks in the filesystem because they are created on the
fly at installation time by the copy_firmware.sh script.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

rt3070.bin

-rt2870.bin
\ No newline at end of file

rt3090.bin

-rt2860.bin
\ No newline at end of file

s2250.fw

-go7007/s2250-2.fw
\ No newline at end of file

s2250_loader.fw

-go7007/s2250-1.fw
\ No newline at end of file

ti-connectivity/wl1271-nvs.bin

-wl127x-nvs.bin
\ No newline at end of file

ti-connectivity/wl12xx-nvs.bin

-wl127x-nvs.bin
\ No newline at end of file