Revert "conf: clean up memory containing secrets before freeing"

Revert "conf: clean up memory containing secrets before freeing"

Adding supposedly secure cleanup for secrets in anything related to the
XML parser is pointless because there are multiple other un-sanitized
copies of the full XML and the XML parser state at the very least.

Similarly in case RPC was used to transport the XML the RPC buffers are
not sanitized.

Additionally this patch was incomplete as it didn't sanitize the
password in the cleanup function for virDomainGraphicsAuthDef.

This reverts commit 51f8130d78fde3201b49c02b7095ff918b6e658a

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>