Remove Dates-related precompiles

Diagnosed to be causing CSV.jl precompile to fail on windows for an
unknown reason (JuliaData/CSV.jl#981).
Removing the precompiles for now until further investigation can be done
to figure out the root cause.

src/precompile.jl

@@ -5,14 +5,14 @@ function _precompile_()
     pos = 1
     val = "123"
     len = length(val)
-    for T in (String, Int32, Int64, Float64, BigFloat, Dates.Date, Dates.DateTime, Bool)
+    for T in (String, Int32, Int64, Float64, BigFloat, Bool)
         for buf in (codeunits(val), Vector(codeunits(val)))
             Parsers.xparse(T, buf, pos, len, options)
             Parsers.xparse(T, buf, pos, len, options, Any)
         end
     end
 
-    for T in (Int32, Int64, Float64, BigFloat, Dates.Date, Dates.DateTime, Bool)
+    for T in (Int32, Int64, Float64, BigFloat, Bool)
         for buf in (val, SubString(val, 1:3), Vector(codeunits(val)), view(Vector(codeunits(val)), 1:3))
             Parsers.tryparse(T, buf, options)
         end