Remove at-__DIR__ macro definition for Julia versions prior to 0.6

Was added in #281.

README.md

@@ -399,8 +399,6 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 ## New macros
 
-* `@__DIR__` has been added ([#18380])
-
 * `@vectorize_1arg` and `@vectorize_2arg` are deprecated on Julia 0.6 in favor
   of the broadcast syntax ([#17302]). `Compat.@dep_vectorize_1arg` and
   `Compat.@dep_vectorize_2arg` are provided so that packages can still provide
@@ -489,7 +487,6 @@ includes this fix. Find the minimum version from there.
 [#17323]: https://github.com/JuliaLang/julia/issues/17323
 [#17623]: https://github.com/JuliaLang/julia/issues/17623
 [#18082]: https://github.com/JuliaLang/julia/issues/18082
-[#18380]: https://github.com/JuliaLang/julia/issues/18380
 [#18484]: https://github.com/JuliaLang/julia/issues/18484
 [#18629]: https://github.com/JuliaLang/julia/issues/18629
 [#18727]: https://github.com/JuliaLang/julia/issues/18727

src/Compat.jl

@@ -87,13 +87,6 @@ end
         eval(mod, :(include_string($code, $fname)))
 end
 
-@static if VERSION < v"0.6.0-dev.528"
-    macro __DIR__()
-        Base.source_dir()
-    end
-    export @__DIR__
-end
-
 # PR #17302
 # Provide a non-deprecated version of `@vectorize_(1|2)arg` macro which defines
 # deprecated version of the function so that the depwarns can be fixed without

test/runtests.jl

@@ -21,9 +21,6 @@ for os in [:apple, :bsd, :linux, :unix, :windows]
     @eval @test Compat.Sys.$(Symbol("is", os))() == $from_base()
 end
 
-# 0.6
-@test @__DIR__() == dirname(@__FILE__)
-
 # PR #17302
 # To be removed when 0.6 support is dropped.
 f17302(a::Number) = a