Revert r290840

This request by the submitter was valid, but unfortunately there is a good deal
of concern over breakage when DESTDIR != / or "", i.e. with release media.
Making this change correct for all cases would make it markedly more complex
than need be

Requested by: bdrewery, ian, imp
PR: 76362

etc/Makefile

@@ -408,7 +408,7 @@ distrib-dirs: ${MTREES:N/*} distrib-cleanup .PHONY
 		    ${METALOG.add} ; \
 	done; true
 .endif
-	${INSTALL_SYMLINK} ${SRCTOP:C/^\///}/sys ${DESTDIR}/sys
+	${INSTALL_SYMLINK} usr/src/sys ${DESTDIR}/sys
 .if ${MK_MAN} != "no"
 	cd ${DESTDIR}${SHAREDIR}/man; \
 	for mandir in man*; do \