remove _unwrap

[jishnub]

This util method is not necessary anymore, as no_offset_view is equivalent to it. This also adds a methods to _no_offset_view to ignore AbstractUnitRanges with Base.OneTo axes and not convert these to UnitRanges. This means types such as Base.OneTo will be preserved.

julia> OffsetArrays.no_offset_view(Base.OneTo(4)) |> typeof
Base.OneTo{Int64}

[codecov]

Codecov Report

Merging #199 (5446df7) into master (3b5b11b) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
- Coverage   98.26%   98.25%   -0.01%     
==========================================
  Files           5        5              
  Lines         288      287       -1     
==========================================
- Hits          283      282       -1     
  Misses          5        5              

Impacted Files	Coverage Δ
src/utils.jl	100.00% <ø> (ø)
src/OffsetArrays.jl	97.95% <100.00%> (+0.01%)	⬆️

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