xfs: consolidate btree block freeing tracepoints

Don't waste memory on extra per-btree block freeing tracepoints when we
can do it from the generic btree code.

With this patch applied, two tracepoints are collapsed into one
tracepoint, with the following effects on objdump -hx xfs.ko output:

Before:

 10 __tracepoints_ptrs 00000b3c  0000000000000000  0000000000000000  00140eb0  2**2
 14 __tracepoints_strings 00005453  0000000000000000  0000000000000000  00168540  2**5
 29 __tracepoints 00010d90  0000000000000000  0000000000000000  0023f5e0  2**5

After:

 10 __tracepoints_ptrs 00000b38  0000000000000000  0000000000000000  001412f0  2**2
 14 __tracepoints_strings 00005433  0000000000000000  0000000000000000  001689a0  2**5
 29 __tracepoints 00010d30  0000000000000000  0000000000000000  0023fe00  2**5

Column 3 is the section size in bytes; removing these two tracepoints
reduces the size of the ELF segments by 132 bytes.

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