sh: Rip out broken kgdb thread support.

The kgdb thread support is woefully out of date (it predates
the pidhash), and needs a complete rewrite before it's useful
again. Just rip it out entirely.

Updating the unified kgdb stub is a more worthwhile endeavour
for anyone that happens to be interested in this, at present
it's just limping along.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Kconfig.debug

@@ -104,10 +104,6 @@ config KGDB_NMI
 	bool "Enter KGDB on NMI"
 	default n
 
-config KGDB_THREAD
-	bool "Include KGDB thread support"
-	default y
-
 config SH_KGDB_CONSOLE
 	bool "Console messages through GDB"
 	depends on !SERIAL_SH_SCI_CONSOLE