Description of problem:
qemu-ga service still active and can work after qemu-guest-agent been removed

Version-Release number of selected component (if applicable):
qemu-guest-agent-5.1.0-9.module+el8.3.0+8182+ac9ced32.x86_64
systemd-239-40.el8.x86_64
libvirt-6.6.0-6.el8.x86_64

How reproducible:
100%

Steps to Reproduce:
1. check qemu-guest-agent service
● qemu-guest-agent.service - QEMU Guest Agent
   Loaded: loaded (/usr/lib/systemd/system/qemu-guest-agent.service; disabled; vendor preset: enabled)
   Active: active (running) since Thu 2020-09-24 15:57:08 CST; 22min ago
 Main PID: 905 (qemu-ga)
    Tasks: 2 (limit: 8164)
   Memory: 2.1M
   CGroup: /system.slice/qemu-guest-agent.service
           └─905 /usr/bin/qemu-ga --method=virtio-serial --path=/dev/virtio-ports/org.qemu.guest_agent.0 --blacklist=guest-file-open,guest-file-close,guest-file-read,guest-file->

Sep 24 15:57:08 server.lab.eng.pek2.redhat.com systemd[1]: Started QEMU Guest Agent.

2. remove qemu-guest-agent package
# yum remove qemu-guest-agent -y

3. check qemu-guest-agent packages
# rpm -q qemu-guest-agent
package qemu-guest-agent is not installed

4. check qemu-guest-agent service
# systemctl status qemu-guest-agent
● qemu-guest-agent.service
   Loaded: not-found (Reason: Unit qemu-guest-agent.service not found.)
   Active: active (running) since Thu 2020-09-24 15:57:08 CST; 34min ago
 Main PID: 905 (qemu-ga)
    Tasks: 2 (limit: 8164)
   Memory: 2.1M
   CGroup: /system.slice/qemu-guest-agent.service
           └─905 /usr/bin/qemu-ga --method=virtio-serial --path=/dev/virtio-ports/org.qemu.guest_agent.0 --blacklist=guest-file-open,guest-file-close,guest-file-read,guest-file->

Sep 24 15:57:08 server.lab.eng.pek2.redhat.com systemd[1]: Started QEMU Guest Agent.
Sep 24 16:31:50 server.lab.eng.pek2.redhat.com systemd[1]: qemu-guest-agent.service: Current command vanished from the unit file, execution of the command list won't be resumed.

5. ping guest using qemu-agent-command
# virsh qemu-agent-command server '{"execute":"guest-info"}' ; echo $?
{"return":{"version":"5.1.0","supported_commands":[{"enabled":true,"name":"guest-get-osinfo","success-response":true},{"enabled":true,"name":"guest-get-timezone","success-response":true}...

0

5. execute some guest agent cmd from host
# virsh domtime server
Time: 1601037719

Expected results:
Check the qemu-guest-agent after uninstallation,
# systemctl status qemu-guest-agent
Unit qemu-guest-agent.service could not be found.

Additional info:
Tried with rhel7.9 os with qemu-guest-agent-2.12.0-3.el7.x86_64, will get 
the expected result.