Revert "Mark DIV/IDIV instructions hasSideEffects=1 because they can trap when dividing by 0. This is needed to keep early if conversion from moving them across basic blocks."

This reverts commit r171461 since it breaks the following tests:

Clang :: Analysis/outofbound-notwork.c
Clang :: Analysis/string-fail.c
Clang :: CXX/basic/basic.lookup/basic.lookup.qual/p6-0x.cpp
Clang :: CXX/basic/basic.lookup/basic.lookup.unqual/p15.cpp
Clang :: CXX/dcl.dcl/dcl.spec/dcl.fct.spec/p4.cpp
Clang :: CXX/dcl.dcl/dcl.spec/dcl.stc/p10.cpp
Clang :: CXX/temp/temp.param/p14.cpp
Clang :: CXX/temp/temp.res/temp.dep.res/temp.point/p1.cpp
Clang :: CodeGen/2009-02-13-zerosize-union-field-ppc.c
Clang :: CodeGen/blocks-2.c
Clang :: CodeGen/libcalls-d.c
Clang :: CodeGen/libcalls-ld.c
Clang :: CodeGenCXX/conversion-function.cpp
Clang :: CodeGenCXX/debug-info-limit-type.cpp
Clang :: CodeGenCXX/inheriting-constructor.cpp
Clang :: FixIt/fixit-errors.c
Clang :: FixIt/fixit-pmem.cpp
Clang :: Modules/namespaces.cpp
Clang :: PCH/changed-files.c
Clang :: PCH/pr4489.c
Clang :: PCH/source-manager-stack.c
Clang :: Parser/cxx-ambig-decl-expr-xfail.cpp
Clang :: SemaCXX/switch-implicit-fallthrough-cxx98.cpp
Clang :: SemaTemplate/instantiate-function-1.mm