classes: remove obsolete classes

classes: remove obsolete classes

All of these classes are currently unused in oe-core and meta-oe; several
are no longer in use even in OE classic:

* base_srpm.bbclass
* ccdv.bbclass
* flow-lossage.bbclass
* patcher.bbclass
* singlemachine.bbclass
* tmake.bbclass
* xlibs.bbclass

patcher.bbclass and singlemachine.bbclass probably still work but it is
unlikely that anyone is still using them.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>