Remove obsolete field in RelocInfo.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1413373004

Cr-Commit-Position: refs/heads/master@{#31622}

src/assembler.h

@@ -662,11 +662,6 @@ class RelocInfo {
   Mode rmode_;
   intptr_t data_;
   Code* host_;
-  // External-reference pointers are also split across instruction-pairs
-  // on some platforms, but are accessed via indirect pointers. This location
-  // provides a place for that pointer to exist naturally. Its address
-  // is returned by RelocInfo::target_reference_address().
-  Address reconstructed_adr_ptr_;
   friend class RelocIterator;
 };