LU-709 build: clean up four macros in lustre-core.m4

LU-709 build: clean up four macros in lustre-core.m4

1. truncate_inode_pages_range() was added since v2.6.15
2. HAVE_RELEASEPAGE_WITH_GFP is not used
3. HAVE_STATFS_NAMELEN is not used
4. HAVE_D_ADD_UNIQUE is not used

Signed-off-by: Peng Tao <peng_tao@emc.com>
Change-Id: I6864d0f18c14f5087b2d1a0c20fcf14f92d7246f
Reviewed-on: http://review.whamcloud.com/2313
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>