pimd: Start cleanup of documentation

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

pimd/WHY_SSM

@@ -1,32 +0,0 @@
-WHY SSM
-
-Benefis of PIM SSM over PIM SM
-------------------------------
-
-- SSM consumes minimum link bandwidth
-- SSM simplifies multicast address management (specially important for
-  inter-domain multicast)
-  - SSM (S,G) channels easily provide unique per-application addressing
-  - SSM does not require MSDP between PIM domains
-- SSM does not suffer instabilities from traffic-driven SPT switchover
-- SSM is not suscetible to DoS attack from unwanted sources
-- SSM does not use RP. Some RP issues:
-  - RP is possible point of failure
-  - RP demands redundancy management
-  - RP may require PIM dense mode support for RP election
-  - RP is possible performance bottleneck
-  - RP may demand lots of extra management
-- SSM can be deployed in an existing PIM SM network (only the last hop
-  routers need to support IGMPv3)
-- SSM is easier to deploy and maintain
-
-PIM-SSM drawbacks
------------------
-
-- SSM requires IGMPv3 support on both receivers and last-hop routers
-- SSM may be memory intensive when managing (S,G) states for
-  many-to-many multicast distribution
-- SSM will keep (S,G) state as long as there are subscriptions from
-  receivers, even if the source is not actually sending traffic
-
---EOF--