Remove IBM copyright

This copyright isn't needed and is not in any other file.
It is not being updated. Just remove it.

Similar changes were done at
https://gerrit.openbmc.org/c/openbmc/bmcweb/+/41139.

This was added in the original commit of this repo:
https://github.com/openbmc/phosphor-user-manager/commit/8a89b53bf014d0844dfd85b2327853037d1e2cb7

Tested: None. Document change only.

Change-Id: Ifc9f73a430af8c5da6174e4c48b318b1bbc41ee5
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
1 file changed