ci: slim down CI Pipeline

Since the totality of sourcehut only has 4 CI slots at the moment, slim
the CI pipeline down to the lowest common denominator:

Linux (alpine-edge)
 - GNU make
 - latest Go version
 - Go1.13
OpenBSD
 - BSD make
 - latest available Go Version (currently lagging behind 1 version)

We might also want to consider changing OpenBSD to FreeBSD as to my
knowledge FreeBSD is the more common Home-Computer-Version of BSD
instead of OpenBSD which is mainly used for servers. (please don't lynch
me, dear 3 OpenBSD people)

Signed-off-by: Moritz Poldrack <git@moritz.sh>
Acked-by: Robin Jarry <robin@jarry.cc>

.builds/alpine-edge.yml

@@ -24,3 +24,7 @@ tasks:
   - test: |
       cd aerc
       go test ./...
+  - ancient-go-version: |
+      go install golang.org/dl/go1.13@latest
+      ~/go/bin/go1.13 download
+      make GO=~/go/bin/go1.13

.builds/debian-stable.yml

@@ -1,23 +0,0 @@
----
-image: debian/stable
-packages:
-  - golang
-  - gnupg2
-  - libnotmuch-dev
-  - scdoc
-sources:
-  - "https://git.sr.ht/~rjarry/aerc"
-environment:
-  DESTDIR: ./out
-  GOFLAGS: "-tags=notmuch"
-tasks:
-  - build: |
-      cd aerc
-      make
-  - install: |
-      cd aerc
-      make install
-      make checkinstall
-  - test: |
-      cd aerc
-      go test ./...

.builds/fedora-latest.yml

@@ -1,23 +0,0 @@
----
-image: fedora/latest
-packages:
-  - golang
-  - gnupg2
-  - notmuch-devel
-  - scdoc
-sources:
-  - "https://git.sr.ht/~rjarry/aerc"
-environment:
-  DESTDIR: ./out
-  GOFLAGS: "-tags=notmuch"
-tasks:
-  - build: |
-      cd aerc
-      make
-  - install: |
-      cd aerc
-      make install
-      make checkinstall
-  - test: |
-      cd aerc
-      go test ./...

.builds/openbsd.yml

@@ -16,6 +16,3 @@ tasks:
       cd aerc
       make install
       make checkinstall
-  - test: |
-      cd aerc
-      go test ./...