Removing block device by-num symlinks

The uevent.partition_num easily collides between partitions, for
example:

  Both /dev/block/sda3 and /dev/block/sdd3 will generate the same symlink:
    /dev/block/platform/soc/1da4000.ufshc/by-num/p3

This change remove those by-num symlinks as there seems no effective
user of it.

Bug: 78613232
Test: m init_tests && \
      adb push $OUT/data/nativetest64/init_tests/init_tests /data/. && \
      adb shell /data/init_tests

Change-Id: I8dfa8dc1a2f9fc9296aa30f33e905bf158b501de
Merged-In: I8dfa8dc1a2f9fc9296aa30f33e905bf158b501de
(cherry picked from commit 95591bd0)