Remove cgo_pthread_ordering_workaround.go

Per https://bugzilla.redhat.com/show_bug.cgi?id=1326903 and
https://sourceware.org/bugzilla/show_bug.cgi?id=19861#c9 , this
was fixed in Glibc 2.24 .

Removing this will also allow us not to worry about LDFLAGS
necessary to make -lgpgme work.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

cmd/skopeo/cgo_pthread_ordering_workaround.go

@@ -1,35 +0,0 @@
-//go:build !containers_image_openpgp
-// +build !containers_image_openpgp
-
-package main
-
-/*
-This is a pretty horrible workaround.  Due to a glibc bug
-https://bugzilla.redhat.com/show_bug.cgi?id=1326903 , we must ensure we link
-with -lgpgme before -lpthread.  Such arguments come from various packages
-using cgo, and the ordering of these arguments is, with current (go tool link),
-dependent on the order in which the cgo-using packages are found in a
-breadth-first search following dependencies, starting from “main”.
-
-Thus, if
-   import "net"
-is processed before
-   import "…/skopeo/signature"
-it will, in the next level of the BFS, pull in "runtime/cgo" (a dependency of
-"net") before "mtrmac/gpgme" (a dependency of "…/skopeo/signature"), causing
--lpthread (used by "runtime/cgo") to be used before -lgpgme.
-
-This might be possible to work around by careful import ordering, or by removing
-a direct dependency on "net", but that would be very fragile.
-
-So, until the above bug is fixed, add -lgpgme directly in the "main" package
-to ensure the needed build order.
-
-Unfortunately, this workaround needs to be applied at the top level of any user
-of "…/skopeo/signature"; it cannot be added to "…/skopeo/signature" itself,
-by that time this package is first processed by the linker, a -lpthread may
-already be queued and it would be too late.
-*/
-
-// #cgo LDFLAGS: -lgpgme
-import "C"