The issue manifests due to a bug in mysql_routine_grant. This was a side
effect of e46eea86 which fixed the problem of not giving appropriate error
message (ER_NONEXISTING_PROC_GRANT) when a routine grant existed due to role
inheritance.

When granting a routine privilege, it is possible to have a GRANT_NAME
entry already created from an inherited role, but with it's init_privs
set to 0.

In this case we must not create a *new* grant entry, but we must edit
this grant entry to set its init_privs.

Note that this case was already covered by MDEV-29458, however due to a
forgotten "flush privileges;" the actual code path never got hit.
Remove the flush privilege command as it was never intended to be there
in the first place.