minor KnpLabs#900 Remove BC check on 3.x (GrahamCampbell)

This PR was squashed before being merged into the 3.0.x-dev branch.

Discussion
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Can be added back once 3.0.0 is tagged.

Commits
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b78cc5b Remove BC check on 3.x
4027cb9 Restore with comment

Author: GrahamCampbell

.travis.yml

@@ -18,9 +18,10 @@ php:
 
 matrix:
   include:
-    - php: 7.4.7
-      name: Backward compatibillity check
-      env: DEPENDENCIES="roave/backward-compatibility-check" TEST_COMMAND="vendor/bin/roave-backward-compatibility-check"
+# BC check disabled until 3.0.0 is tagged
+#     - php: 7.4.7
+#       name: Backward compatibillity check
+#       env: DEPENDENCIES="roave/backward-compatibility-check" TEST_COMMAND="vendor/bin/roave-backward-compatibility-check"
     - php: 7.4
       name: phpstan
       script: