Remove old code

Author: dlfivefifty

src/AbstractFFTs.jl

@@ -8,9 +8,4 @@ export fft, ifft, bfft, fft!, ifft!, bfft!,
 include("definitions.jl")
 include("TestUtils.jl")
 
-if !isdefined(Base, :get_extension)
-    include("../ext/AbstractFFTsChainRulesCoreExt.jl")
-    include("../ext/AbstractFFTsTestExt.jl")
-end
-
 end # module

test/runtests.jl

@@ -202,7 +202,7 @@ end
                 # type inference checks of `rrule` fail on old Julia versions
                 # for higher-dimensional arrays:
                 # https://github.com/JuliaMath/AbstractFFTs.jl/pull/58#issuecomment-916530016
-                check_inferred = ndims(x) < 3 || VERSION >= v"1.6"
+                check_inferred = ndims(x) < 3
 
                 test_frule(AbstractFFTs.fftshift, x, dims)
                 test_rrule(AbstractFFTs.fftshift, x, dims; check_inferred=check_inferred)