[llvm] [docs] remove some out-of-date content in LLVM Programmer's Manual (PR #74989)

[Duncan P. N. Exon Smith via llvm-commits]

================
@@ -2779,17 +2761,9 @@ obtaining it via iteration over some structure:
     if (it != inst->getParent()->end()) errs() << *it << "\n";
   }
 
-Unfortunately, these implicit conversions come at a cost; they prevent these
-iterators from conforming to standard iterator conventions, and thus from being
-usable with standard algorithms and containers.  For example, they prevent the
-following code, where ``B`` is a ``BasicBlock``, from compiling:
-
-.. code-block:: c++
-
-  llvm::SmallVector<llvm::Instruction *, 16>(B->begin(), B->end());
-
-Because of this, these implicit conversions may be removed some day, and
-``operator*`` changed to return a pointer instead of a reference.
+..
+  The part about implicit conversion from an iterator to a pointer is out of
+  date and has been removed.
----------------
dexonsmith wrote:

That's considerate, but I agree with @nickdesaulniers that we don't need to be so cautious. Let's just describe the current state accurately. (If we documented all the things we removed we wouldn't have space for the stuff that's still here!)

https://github.com/llvm/llvm-project/pull/74989