Remove some dependencies of distclean on clean. This should not be necessary...

Remove some dependencies of distclean on clean.  This should not be necessary in higher level makefiles and should speed up make distclean

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5453 42af7a65-404d-4744-a932-0658087f49c3