(incorrect, do not land!) clang-format: Delete dead code

[thakis]

Summary

This is wrong (see r366926); I'm just uploading it for my notes

---

IsExpression set on the context affects ony what determineStarAmpUsage()
does. For if and while, the result of determineStarAmpUsage() is always
ignored in practice:

• As of r172731, parseParens() overwrites the result with TT_BinaryOperator for * and & (and &&, added later) for the first occurrence in parens that has an identifier on both sides and that doesnn't look like a <op> b =. (Later r212040 propagated this to all later binary operators in the parens).

• As of r173256, modifyContext() (called determineTokenType() back then) converts * & && to the left of assignment operators to TT_PointerOrReference.

So in ifs and whiles, all initial token types get overwritten.

The kw_if and kw_while that this is removing were added in r188256,
which was after these two changes. However, r220805 later made the
case motivating this addition work in a different way.

(XXX C++17 initial-statements?)

clang/lib/Format/TokenAnnotator.cpp

if (Left->is(TT_OverloadedOperatorLParen)) {
                (Line.startsWith(Keywords.kw_type, tok::identifier) ||
                 Line.startsWith(tok::kw_export, Keywords.kw_type,
                                 tok::identifier))) {
       // type X = (...);
       // export type X = (...);
       Contexts.back().IsExpression = false;
     } else if (Left->Previous &&
                (Left->Previous->isOneOf(tok::kw_static_assert, tok::kw_decltype,
-                                        tok::kw_if, tok::kw_while, tok::l_paren,
-                                        tok::comma) ||
-                Left->Previous->endsSequence(tok::kw_constexpr, tok::kw_if) ||
+                                        tok::l_paren, tok::comma) ||
                 Left->Previous->is(TT_BinaryOperator))) {
-      // static_assert, if and while usually contain expressions.
+      // static_assert and decltype while usually contain expressions.
       Contexts.back().IsExpression = true;
     } else if (Style.Language == FormatStyle::LK_JavaScript && Left->Previous &&
                (Left->Previous->is(Keywords.kw_function) ||
                 (Left->Previous->endsSequence(tok::identifier,
                                               Keywords.kw_function)))) {
       // function(...) or function f(...)
       Contexts.back().IsExpression = false;
     } else if (Style.Language == FormatStyle::LK_JavaScript && Left->Previous &&
bool rParenEndsCast(const FormatToken &Tok) {
     for (FormatToken *Prev = Tok.Previous; Prev != Tok.MatchingParen;
          Prev = Prev->Previous) {
       if (!Prev->isOneOf(tok::kw_const, tok::identifier, tok::coloncolon))
         return false;
     }
     return true;
   }
 
-  /// Return the type of the given token assuming it is * or &.
+  /// Return the type of the given token assuming it is *, &, or &&.
   TokenType determineStarAmpUsage(const FormatToken &Tok, bool IsExpression,
                                   bool InTemplateArgument) {
     if (Style.Language == FormatStyle::LK_JavaScript)
       return TT_BinaryOperator;
 
     const FormatToken *PrevToken = Tok.getPreviousNonComment();
     if (!PrevToken)
       return TT_UnaryOperator;