[AST] Remove AccessorDecl handling from getSourceRangeIncludingAttrs

It doesn't seem like this is necessary anymore since we no longer
clone OverrideAttrs when checking overrides (except when
invalidating). Moreover, it's now actively wrong since accessors
introduced by macro expansions may be in different buffers than their
their storage, so checking `isBeforeInBuffer` will non-deterministically
result in the wrong source range.

Author: hamishknight

lib/AST/Decl.cpp

@@ -966,26 +966,6 @@ case DeclKind::ID: return cast<ID##Decl>(this)->getSourceRange();
 SourceRange Decl::getSourceRangeIncludingAttrs() const {
   auto Range = getSourceRange();
 
-  // Attributes on AccessorDecl may syntactically belong to PatternBindingDecl.
-  // e.g. 'override'.
-  if (auto *AD = dyn_cast<AccessorDecl>(this)) {
-    // If this is implicit getter, accessor range should not include attributes.
-    if (AD->isImplicitGetter())
-      return Range;
-
-    // Otherwise, include attributes directly attached to the accessor.
-    SourceLoc VarLoc = AD->getStorage()->getStartLoc();
-    for (auto *Attr : getParsedAttrs()) {
-      if (!Attr->getRange().isValid())
-        continue;
-
-      SourceLoc AttrStartLoc = Attr->getRangeWithAt().Start;
-      if (getASTContext().SourceMgr.isBeforeInBuffer(VarLoc, AttrStartLoc))
-        Range.widen(AttrStartLoc);
-    }
-    return Range;
-  }
-
   // Attributes on VarDecl syntactically belong to PatternBindingDecl.
   if (isa<VarDecl>(this) && !isa<ParamDecl>(this))
     return Range;