ath79: don't include tl-wdr3600 image build code for tl-wdr4300
Including the tl-wdr3600 image build code just to overwrite most of it
doesn't make much sense and only makes it hard to read.
Furthermore, the tl-wdr4300 image will be marked as compatible with the
tl-wdr3600 this way.
Signed-off-by: Mathias Kresin <[email protected]>
Mathias Kresin