[IR] Remove support for insertvalue constant expression

This removes the insertvalue constant expression, as part of
https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179.
This is very similar to the extractvalue removal from D125795.
insertvalue is also not supported in bitcode, so no auto-ugprade
is necessary.

ConstantExpr::getInsertValue() can be replaced with
IRBuilder::CreateInsertValue() or ConstantFoldInsertValueInstruction(),
depending on whether a constant result is required (with the latter
being fallible).

The ConstantExpr::hasIndices() and ConstantExpr::getIndices()
methods also go away here, because there are no longer any constant
expressions with indices.

Differential Revision: https://reviews.llvm.org/D128719

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -2674,9 +2674,6 @@ void ModuleBitcodeWriter::writeConstants(unsigned FirstVal, unsigned LastVal,
         Record.push_back(VE.getValueID(C->getOperand(1)));
         Record.push_back(CE->getPredicate());
         break;
-      case Instruction::InsertValue:
-        report_fatal_error("insertvalue constexprs not supported");
-        break;
       }
     } else if (const BlockAddress *BA = dyn_cast<BlockAddress>(C)) {
       Code = bitc::CST_CODE_BLOCKADDRESS;