Revert "Put build artifacts in debian/build/ to avoid polluting upstream sources"

This reverts commit 0bdd05c.

While the general idea makes sense and would make things better, this
had some push back on the review and still got merged anyway. It also
conflicts with an old proposal that still is pending to be updated
and re-proposed to try to unify the build paths for all packages at the
dpkg and debhelper layer, via a new dpkg-build-api level. And doing a
migration twice seems wasteful.

Ref: https://lists.debian.org/debian-dpkg/2020/03/msg00003.html

Author: guillemj

template.go

@@ -86,7 +86,6 @@ func writeDebianGitIgnore(dir, debLib, debProg string, pkgType packageType) erro
 	fmt.Fprintf(f, "*.log\n")
 	fmt.Fprintf(f, "*.substvars\n")
 	fmt.Fprintf(f, "/.debhelper/\n")
-	fmt.Fprintf(f, "/build/\n")
 	fmt.Fprintf(f, "/debhelper-build-stamp\n")
 	fmt.Fprintf(f, "/files\n")
 
@@ -300,12 +299,7 @@ func writeDebianRules(dir string, pkgType packageType) error {
 	fmt.Fprintf(f, "#!/usr/bin/make -f\n")
 	fmt.Fprintf(f, "\n")
 	fmt.Fprintf(f, "%%:\n")
-	fmt.Fprintf(f, "\tdh $@ --builddirectory=debian/build --buildsystem=golang\n")
-	// Note: The above `--builddirectory=debian/build` will eventually be obsolete
-	// in 2028+ then the dh-golang version 1.63+ that has
-	// https://salsa.debian.org/go-team/packages/dh-golang/-/commit/bc16dff5381b668a71fa99c381baba202c34c789
-	// is in use everywhere
-
+	fmt.Fprintf(f, "\tdh $@ --builddirectory=_build --buildsystem=golang\n")
 	if pkgType == typeProgram {
 		fmt.Fprintf(f, "\n")
 		fmt.Fprintf(f, "override_dh_auto_install:\n")