rtld: don't add extraneous -L directory when MK_TOOLCHAIN == no

rtld's Makefile used to add -L${LIBDIR} to LDFLAGS when MK_TOOLCHAIN was
no.  This was done as part of a change to fix building rtld with
MK_TOOLCHAIN == no (although I'm not sure this part was necessary).

In any case as of 5f2e84015d libc_pic.a is built independent of the
MK_TOOLCHAIN setting and the main part of the workaround has already
been removed.  Remove the rest now.

This reverts commit c0f5aeb032.

Reviewed by:	jrtc27
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D39938

libexec/rtld-elf/Makefile

@@ -57,9 +57,6 @@ CFLAGS+=	-fpic -DPIC $(DEBUG)
 LDFLAGS+=	-shared -Wl,-Bsymbolic -Wl,-z,defs -nostdlib -e ${RTLD_ENTRY}
 # Pull in the dependencies that we use from libc
 .include "rtld-libc/Makefile.inc"
-.if ${MK_TOOLCHAIN} == "no"
-LDFLAGS+=	-L${LIBCDIR}
-.endif
 
 VERSION_DEF=	${LIBCSRCDIR}/Versions.def
 SYMBOL_MAPS=	${RTLD_ELF_DIR}/Symbol.map