mediatek: Remove modules.builtin file

This file should be generated automatically at runtime by the kernel
build system.

Link: https://github.com/openwrt/openwrt/pull/19473
(cherry picked from commit e53c53b7d59d444a7964fbeaa66609f13c1133f9)
Link: https://github.com/openwrt/openwrt/pull/19839
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/mediatek/files/drivers/net/phy/rtk/modules.builtin

@@ -1 +0,0 @@
-kernel/drivers/net/phy/rtk/rtl8367s_gsw.ko