Remove old $Code argument, and stop passing $Why up to Header

$Code was excised in RT 2.1, in 4137c44, which also removed any reason
to pass $Why to the header.
Remove <%cleanup> block, which just obfuscates things
Remove WebRT prefix on error messages in logs

WebRT is a concept which dates back to RT 2 days, and has no meaning
Remove SelfService/Error.html, replacing with standard Abort() calls
Merge branch '4.2/error-cleanup'

Conflicts:
	share/html/SelfService/Display.html