[clang-tidy][NFC] Remove unnecessary nullptr check on cast subexpr (llvm#85473)

The value of SubExpr is not null since getSubExpr would assert in that
case. Remove the nullptr check. This avoids confusion since SubExpr is
used without check later in the function.

Author: mikerice1969

clang-tools-extra/clang-tidy/readability/ImplicitBoolConversionCheck.cpp

@@ -81,8 +81,7 @@ void fixGenericExprCastToBool(DiagnosticBuilder &Diag,
 
   const Expr *SubExpr = Cast->getSubExpr();
 
-  bool NeedInnerParens =
-      SubExpr != nullptr && utils::fixit::areParensNeededForStatement(*SubExpr);
+  bool NeedInnerParens = utils::fixit::areParensNeededForStatement(*SubExpr);
   bool NeedOuterParens =
       Parent != nullptr && utils::fixit::areParensNeededForStatement(*Parent);