In order for parameter attribute uniquing to make

any sense it is important that ParamAttr::None gets
treated the same as not supplying an attribute at
all.  Rather than stripping ParamAttr::None out of
the list of attributes, assert if ParamAttr::None
is seen.  Fix up the bitcode reader which liked to
insert ParamAttr::None all over the place.  Patch
based on one by Török Edwin.

llvm-svn: 44250