add type annotations for non-constant Base globals (JuliaLang/julia#44166)

* add type annotations for non-constant Base globals
* remove no-longer needed callsite annotations

Author: aviatesk

src/cluster.jl

@@ -531,7 +531,7 @@ default_addprocs_params(::ClusterManager) = default_addprocs_params()
 default_addprocs_params() = Dict{Symbol,Any}(
     :topology => :all_to_all,
     :dir      => pwd(),
-    :exename  => joinpath(Sys.BINDIR::String, julia_exename()),
+    :exename  => joinpath(Sys.BINDIR, julia_exename()),
     :exeflags => ``,
     :enable_threaded_blas => false,
     :lazy => true)