backlight: qcom-wled: Remove unused configs for LED3 and LED4

Fixes W=1 warnings:

 drivers/video/backlight/qcom-wled.c:1294:34: warning: ‘wled4_string_cfg’ defined but not used [-Wunused-const-variable=]
 1294 | static const struct wled_var_cfg wled4_string_cfg = {
 | ^~~~~~~~~~~~~~~~
 drivers/video/backlight/qcom-wled.c:1290:34: warning: ‘wled3_string_cfg’ defined but not used [-Wunused-const-variable=]
 1290 | static const struct wled_var_cfg wled3_string_cfg = {
 | ^~~~~~~~~~~~~~~~

Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: linux-arm-msm@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>