Respect multilib directories

--- src/aaa_lib/Makefile.am
+++ src/aaa_lib/Makefile.am
@@ -18,7 +18,6 @@
 AQUA_LIBS = ${top_builddir}/contrib/aqua/libapbsaqua.la
 BLAS_LIBS = @blas_lib@
 
-libdir = ${prefix}/lib
 lib_LTLIBRARIES = libapbs.la
 
 libapbs_la_SOURCES = apbs_link.c
--- bin/Makefile.am
+++ bin/Makefile.am
@@ -27,7 +27,6 @@
 rm.apbs: Makefile
 	-rm -f apbs
 
-libdir = ${prefix}/lib
 lib_LTLIBRARIES = libapbsmainroutines.la
 libapbsmainroutines_la_SOURCES = routines.c
 libapbsmainroutines_la_LDFLAGS = -version-info ${APBS_VERSION}