Issue #3840: Arch added a mypaint-brushes1 package.

This is the base system for our CI, and the former mypaint-brushes
package got bumped to v2, which broke the build. Instead of rolling
back, they added a mypaint-brushes1 package. Let's rely on it instead of
installing it ourselves now.

.gitlab-ci.yml

@@ -1,7 +1,6 @@
 image: archlinux/base:latest
 
 stages:
-  - mypaint-brushes
   - babl
   - gegl
   - gimp
@@ -15,30 +14,6 @@ cache:
   paths:
   - _pacman_cache
 
-.mypaint-brushes-base:
-  stage: mypaint-brushes
-  artifacts:
-    paths:
-    - "${INSTALL_DIR}"
-  variables:
-    GIT_DEPTH: "5"
-  before_script:
-    - pacman -Syu --noconfirm --needed --cachedir "${PACMAN_CACHE}"
-        git
-        base-devel
-    - git clone --branch=v1.3.x --depth="${GIT_DEPTH}" https://github.com/mypaint/mypaint-brushes.git _mypaint-brushes
-
-mypaint-brushes-git:
-  extends: .mypaint-brushes-base
-  script:
-    - cd _mypaint-brushes
-    - ./autogen.sh
-    - mkdir _build
-    - cd _build
-    - ../configure
-        --prefix="${INSTALL_PREFIX}"
-    - make install
-
 .babl-base:
   stage: babl
   artifacts:
@@ -169,7 +144,7 @@ gegl-git:
         libwmf
         libxmu
         libxpm
-        mypaint-brushes
+        mypaint-brushes1
         openexr
         poppler-data
         pygtk
@@ -206,7 +181,6 @@ gegl-git:
 build-git-autotools:
   extends: .gimp-autotools
   dependencies:
-    - mypaint-brushes-git
     - babl-git
     - gegl-git