Revert [DSE] Preserve basic block ordering using OrderedBasicBlock.

This reverts r357208 (git commit c0bfd37d)

This causes a buildbot failure:  http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/16124

FAILED: lib/IR/CMakeFiles/LLVMCore.dir/IRBuilder.cpp.o
/home/buildslave/ps4-buildslave1/clang-with-thin-lto-ubuntu/install/stage2/bin/clang++   -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Ilib/IR -I/home/buildslave/ps4-buildslave1/clang-with-thin-lto-ubuntu/llvm.src/lib/IR -Iinclude -I/home/buildslave/ps4-buildslave1/clang-with-thin-lto-ubuntu/llvm.src/include -fPIC -fvisibility-inlines-hidden -Werror -Werror=date-time -Werror=unguarded-availability-new -std=c++11 -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fdiagnostics-color -ffunction-sections -fdata-sections -flto=thin -O3    -UNDEBUG  -fno-exceptions -fno-rtti -MD -MT lib/IR/CMakeFiles/LLVMCore.dir/IRBuilder.cpp.o -MF lib/IR/CMakeFiles/LLVMCore.dir/IRBuilder.cpp.o.d -o lib/IR/CMakeFiles/LLVMCore.dir/IRBuilder.cpp.o -c /home/buildslave/ps4-buildslave1/clang-with-thin-lto-ubuntu/llvm.src/lib/IR/IRBuilder.cpp
clang-9: /home/buildslave/ps4-buildslave1/clang-with-thin-lto-ubuntu/llvm.src/lib/Analysis/OrderedBasicBlock.cpp:38: bool llvm::OrderedBasicBlock::comesBefore(const llvm::Instruction *, const llvm::Instruction *): Assertion `!(LastInstFound == BB->end() && NextInstPos != 0) && "Instruction supposed to be in NumberedInsts"' failed.

llvm-svn: 357211