Remove a couple of Stream flags

Summary:
I came across this while trying to understand what Log::Debug does. It turns out
it does not do anything, as there is no instance of someone setting a debug flag
on a stream. The same is true for the Verbose and AddPrefix flags. Removing
these will enable some cleanups in the Logging class, and it brings us closer
towards the long term goal of standardizing on llvm stream classes.

I have removed these flags and all code the code which tested for their
presence -- there wasn't much of it, mostly in SymbolFileDWARF, which is
probably going away at some point anyway.

The eBinary flag still has some users, so I am letting it life for the time
being.

Reviewers: clayborg, zturner

Subscribers: aprantl, beanz, lldb-commits

Differential Revision: https://reviews.llvm.org/D28616

llvm-svn: 291895