Dropped LFS_T_MTREEONLY from all APIs except lfsr_traversal_t

Looking at future planned features, we're running into some real issues
fitting all these flags into 32 bits.

I think the only real use case for LFS_T_MTREEONLY is in
lfsr_traversal_t, where the depth of traversal can't be infered. So no
reason to keep this flag around in the other APIs.

No code changes:

                   code          stack          ctx
  default before: 37804           2608          620
  default after:  37804 (+0.0%)   2608 (+0.0%)  620 (+0.0%)

  gc before:      37940           2608          768
  gc after:       37940 (+0.0%)   2608 (+0.0%)  768 (+0.0%)

lfs.h

@@ -173,7 +173,6 @@ enum lfs_type {
                         0x08000000  // Check data checksums on reads
 #endif
 
-#define LFS_F_MTREEONLY 0x00000800  // Only traverse the mtree
 #define LFS_F_COMPACT   0x00008000  // Compact metadata logs
 #define LFS_F_CKMETA    0x00010000  // Check metadata checksums
 #define LFS_F_CKDATA    0x00020000  // Check metadata + data checksums
@@ -197,7 +196,6 @@ enum lfs_type {
                         0x08000000  // Check data checksums on reads
 #endif
 
-#define LFS_M_MTREEONLY 0x00000800  // Only traverse the mtree
 #define LFS_M_MKCONSISTENT \
                         0x00001000  // Make the filesystem consistent
 #define LFS_M_LOOKAHEAD 0x00002000  // Populate lookahead buffer
@@ -257,8 +255,6 @@ enum lfs_btype {
 #define LFS_T_MUTATED   0x00000200  // Filesystem modified by traversal
 
 // GC flags
-#define LFS_GC_MTREEONLY \
-                        0x00000800  // Only traverse the mtree
 #define LFS_GC_MKCONSISTENT \
                         0x00001000  // Make the filesystem consistent
 #define LFS_GC_LOOKAHEAD \