libc: remove .PATH refs to libc/<arch>/sys

There are no longer any source files here so remove references.

Reviewed by:	kib, emaste, imp
Pull Request:	https://github.com/freebsd/freebsd-src/pull/908

lib/libc/powerpcspe/sys/Makefile.inc

@@ -1,3 +1,2 @@
-.PATH: ${LIBC_SRCTOP}/powerpc/sys
 .PATH: ${LIBSYS_SRCTOP}/powerpc
 .sinclude "${LIBC_SRCTOP}/powerpc/sys/Makefile.inc"

lib/libc/x86/sys/Makefile.inc

@@ -1,4 +1,3 @@
-.PATH:	${LIBC_SRCTOP}/x86/sys
 .PATH:	${LIBSYS_SRCTOP}/x86
 
 SRCS+= \

lib/libsys/Makefile.sys

@@ -1,6 +1,5 @@
 
 # sys sources
-.PATH: ${LIBC_SRCTOP}/${LIBC_ARCH}/sys
 .PATH: ${LIBSYS_SRCTOP}/${LIBC_ARCH} ${LIBSYS_SRCTOP}
 
 # Include the generated makefile containing the *complete* list