configure: Tidy up remnants of non-64-bit physaddrs

Tidy up some remnants of code to support non-64-bit physaddrs
which were accidentally omitted from commit 4be403c8.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

configure

@@ -3733,7 +3733,6 @@ case "$target_arch2" in
   ;;
   x86_64)
     TARGET_BASE_ARCH=i386
-    target_phys_bits=64
     target_long_alignment=8
   ;;
   alpha)
@@ -3836,7 +3835,6 @@ case "$target_arch2" in
     target_long_alignment=8
   ;;
   unicore32)
-    target_phys_bits=32
   ;;
   xtensa|xtensaeb)
     TARGET_ARCH=xtensa