modprobe: shouldn't load kernel modules from /system

Kernel modules are not permitted to be on /system partition.
That was one of Treble requirements in O:
https://source.android.com/devices/architecture/kernel/modular-kernels#file-locations

Bug: 74069409
Test: pixel/nexus devices don't have LKMs in /system, so this change
shoudl be harmless.
Test: walleye boots without issues from modprobe.
Merged-In: I8b3aeb55aacb3c99e0486224161d09a64bb52cd1
Change-Id: I8b3aeb55aacb3c99e0486224161d09a64bb52cd1

(cherry picked from commit 6ef9f523)

public/modprobe.te

@@ -7,5 +7,3 @@ recovery_only(`
   allow modprobe rootfs:system module_load;
   allow modprobe rootfs:file r_file_perms;
 ')
-allow modprobe { system_file }:system module_load;
-r_dir_file(modprobe, { system_file })