blktap: Remove __RD* macros

The __RD* macros are already defined in Xen's io/ring.h which is
included through blkif.h and they have been there for years.  In Xen
4.18 the macros changed for MISRA and now the definitions are out of
sync leading to redefinition errors.  Just remove the local versions and
rely on the io/ring.h ones.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>

Author: jandryuk

drivers/tapdisk-blktap.c

@@ -61,12 +61,6 @@
 #define WARN(_f, _a...)      tlog_syslog(TLOG_WARN, "WARNING: "_f "in %s:%d", \
 					 ##_a, __func__, __LINE__)
 
-#define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
-#define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
-#define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
-#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
-#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
-
 #define BLKTAP_RD32(_n)      __RD32(_n)
 #define BLKTAP_RING_SIZE     __BLKTAP_RING_SIZE(PAGE_SIZE)