mimir: drop pre-built kernel

<?xml version="1.0" encoding="UTF-8"?>

<manifest>

  <project name="e/devices/android_device_volla_mimir" path="device/volla/mimir" remote="e-priv" />

  <project name="e/devices/android_device_volla_mimir-kernel" path="device/volla/mimir-kernel" remote="e-priv" />

  <project name="e/devices/android_kernel_volla_mt8781" path="kernel/volla/mt8781" remote="e-priv" />

  <project name="e/devices/android_device_mediatek_sepolicy-vndr" path="device/mediatek/sepolicy_vndr" remote="e" revision="a14-teracube" />

  <project name="e/devices/android_hardware_mediatek" path="hardware/mediatek" remote="e" />