[XRay] Unsupport version<2 sled entry

[MaskRay]

Summary

For many features we expect clang and compiler-rt to have a version lock
relation, yet for XRaySledEntry we have kept version<2 compatibility for more
than 2 years (I migrated away the last user mips in 2020-09 (D87977)).
I think it's fair to call an end to version<2 now. This should discourage more
work on version<2 (e.g. D140725).

[ianlevesque]

Makes sense to me

compiler-rt/lib/xray/xray_interface_internal.h

 #if SANITIZER_WORDSIZE == 64
   uint64_t Address;
   uint64_t Function;
   unsigned char Kind;
   unsigned char AlwaysInstrument;
   unsigned char Version;
   unsigned char Padding[13]; // Need 32 bytes
   uint64_t function() const {
-    if (Version < 2)
-      return Function;
     // The target address is relative to the location of the Function variable.
     return reinterpret_cast<uint64_t>(&Function) + Function;
   }
   uint64_t address() const {
-    if (Version < 2)
-      return Address;
     // The target address is relative to the location of the Address variable.
     return reinterpret_cast<uint64_t>(&Address) + Address;
   }
 #elif SANITIZER_WORDSIZE == 32
   uint32_t Address;
   uint32_t Function;
   unsigned char Kind;
   unsigned char AlwaysInstrument;
   unsigned char Version;
   unsigned char Padding[5]; // Need 16 bytes
   uint32_t function() const {
-    if (Version < 2)
-      return Function;
     // The target address is relative to the location of the Function variable.
     return reinterpret_cast<uint32_t>(&Function) + Function;
   }
   uint32_t address() const {
-    if (Version < 2)
-      return Address;
     // The target address is relative to the location of the Address variable.
     return reinterpret_cast<uint32_t>(&Address) + Address;
   }
 #else
 #error "Unsupported word size."
 #endif
 };