Remove useless in() methods (JuliaData#128)

These are not actually needed for standard collections, which rely on isequal() or == and hash().
They create ambiguities and can even be incorrect, e.g. for ObjectIdDict. They could even be less
efficient than the default if we stored hashes and implemented optimized hash(::CatValue, ::UInt)
methods. For reference, they have been introduced in 9638d31.

Author: nalimilan

src/value.jl

@@ -115,8 +115,6 @@ Base.isequal(x::Any, y::CatValue) = isequal(y, x)
 Base.isequal(::CatValue, ::Missing) = false
 Base.isequal(::Missing, ::CatValue) = false
 
-Base.in(x::CatValue, y::Any) = get(x) in y
-Base.in(x::CatValue, y::Set) = get(x) in y
 Base.in(x::CatValue, y::AbstractRange{T}) where {T<:Integer} = get(x) in y
 
 Base.hash(x::CatValue, h::UInt) = hash(get(x), h)