Stop error level logging on deleting cgroup file

What

Instead of returning error of files in process directory, log the path on an info level.

Why

In production, we are seeing logs below that end up being noise and not really useful:

{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/cpuacct.usage_percpu_user","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/cpuacct.usage_sys","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/cpuacct.usage_user","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/notify_on_release","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/tasks","time":"2022-09-22T22:03:57.874Z"}

PruneOldGitalyProcessDirectories function is used in 2 different contexts;

1. Delete the cgroup directory under the hierarchy_root for example /gitaly. Inside the cgroup directory there is always files like cpu.stat which can't be deleted.
2. Delete the runtime directory where if there are files in that directory we ignore.

In !4891 (comment 1117227167) we discussed if moving the cgroup deletion into a seperate method but that would be a lot of code duplication, instead change the log level to be info rather then error There error handling is only to log the error message and we don't have any other code path that we execute,

Reference: https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16270