Revert "xfstests: fix to build src/realpath and the correct the existence of target devices"

This reverts commit b03c662399 which overrode
the 0a818862bb xfstests: support post-udev
device mapper node.

Signed-off-by: Rich Johnston <rjohnston@sgi.com>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>

common.config

@@ -221,11 +221,11 @@ else
 fi
 
 # Scripts just don't deal well with symlinked devices
-if [ -L "$TEST_DEV" ]; then
+if [ -L $TEST_DEV ]; then
         TEST_DEV=`src/realpath $TEST_DEV`
 fi
 
-if [ -L "$SCRATCH_DEV" ]; then
+if [ -L $SCRATCH_DEV ]; then
         SCRATCH_DEV=`src/realpath $SCRATCH_DEV`
 fi