[librsvg] CI: remove some rustc jobs.

[Jordan Petridis <jpetridis src gnome org>]

commit 06e8ef2d449fe714bc9554ce1928a54cdd38b9e7
Author: Jordan Petridis <jordanpetridis protonmail com>
Date:   Tue Jun 12 18:28:52 2018 +0000

    CI: remove some rustc jobs.
    
    6dd00f4f bumped the minimum rustc version to 1.24

 .gitlab-ci.yml | 21 ---------------------
 1 file changed, 21 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 3feef41f..31e5e304 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -206,27 +206,6 @@ debian:testing_release_i386:
 # STAGE 3 RUSTC TESTS
 #######################################################################
 
-rustc:1_21:
-  image: $RUSTC_1_21
-  variables:
-    LIBRSVG_DEBUG: "yes"
-  <<: *rustc
-  <<: *stage_3
-
-rustc:1_22:
-  image: $RUSTC_1_22
-  variables:
-    LIBRSVG_DEBUG: "yes"
-  <<: *rustc
-  <<: *stage_3
-
-rustc:1_23:
-  image: $RUSTC_1_23
-  variables:
-    LIBRSVG_DEBUG: "yes"
-  <<: *rustc
-  <<: *stage_3
-
 rustc:1_24:
   image: $RUSTC_1_24
   variables: