Refactor GT_IND value-numbering

Refactor GT_IND value-numbering

Method `fgValueNumberTree` had two pieces of code each attempting to
assume responsibility for `GT_IND` and some block ops.  The one later in
the function wasn't reachable because those ops would always take the
first path.  This change moves the special logic for `GTF_IND_ARR_LEN`,
which was only present in the unreachable code, up to the reachable code,
and removes the unreachable code.

Commit migrated from https://github.com/dotnet/coreclr/commit/f178e60b6c7d41698eeb4f04962307803f78137b