remove extraneous using .Libdl in Libc (#50672)

From f935125

---------

Co-authored-by: Elliot Saba <staticfloat@gmail.com>

Author: vtjnash

base/libc.jl

@@ -487,6 +487,5 @@ geteuid() = ccall(:jl_geteuid, Culong, ())
 
 # Include dlopen()/dlpath() code
 include("libdl.jl")
-using .Libdl
 
 end # module

base/loading.jl

@@ -1027,8 +1027,8 @@ function find_all_in_cache_path(pkg::PkgId)
     end
 end
 
-ocachefile_from_cachefile(cachefile) = string(chopsuffix(cachefile, ".ji"), ".", Base.Libc.dlext)
-cachefile_from_ocachefile(cachefile) = string(chopsuffix(cachefile, ".$(Base.Libc.dlext)"), ".ji")
+ocachefile_from_cachefile(cachefile) = string(chopsuffix(cachefile, ".ji"), ".", Libc.Libdl.dlext)
+cachefile_from_ocachefile(cachefile) = string(chopsuffix(cachefile, ".$(Libc.Libdl.dlext)"), ".ji")
 
 
 # use an Int counter so that nested @time_imports calls all remain open