doc: remove confusing docs about aggregate allocation ratios

Change Ifaf596a8572637f843f47daf5adce394b0365676 added a note
about the behavior change in Ocata where allocation ratios
set on host aggregates was ignored because of placement resource
provider allocation ratios being used.

Later, change I7d8e822cd40dccaf5244e2cd95fa1af43fa9ed87 added
a lot more detail about allocation ratios in the scheduler docs
including the initial* allocation ratio config options. The note
from the previous change was moved and as a result leads to some
confusion since the doc starts by saying essentially, "you can
use these aggregate filters to manage allocation ratios on a set
of hosts" and then the immediate note says essentially, "oh btw
that doesn't work since ocata, sorry!".

To avoid the confusion, this simply removes the part about how
the aggregate filters can be used to manage allocation ratios.

Conflicts:
      doc/source/admin/configuration/schedulers.rst

NOTE(mriedem): The conflict is due to not having change
I8a0d332877fbb9794700081e7954f2501b7e7c09 in Stein.

Change-Id: I62710b0b8c098cca3f67020f4a6da5e684115414
Related-Bug: #1804125
(cherry picked from commit 77efc084fc)

doc/source/admin/configuration/schedulers.rst

@@ -1367,12 +1367,6 @@ The (deprecated) `CoreFilter`_, `DiskFilter`_ and `RamFilter`_ filters will use
 the allocation ratio from the compute node directly when calculating available
 capacity on a given node during scheduling.
 
-The `AggregateCoreFilter`_, `AggregateDiskFilter`_ and `AggregateRamFilter`_
-filters allow overriding per-compute allocation ratios by setting an allocation
-ratio value using host aggregate metadata. This provides a convenient way to
-manage a group of compute hosts with similar allocation ratios while leaving
-the configuration settings alone.
-
 .. _bug-1804125:
 
 .. note:: Regarding the `AggregateCoreFilter`_, `AggregateDiskFilter`_ and