xfs: remove rt-wrappers from xfs_format.h

xfs_format.h has a bunch odd wrappers for helper functions and mount
structure access using RT* prefixes.  Replace them with their open coded
versions (for those that weren't entirely unused) and remove the wrappers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>