Remove 8fips from our runtime matrix

The relevant handling part has been removed in infra, FIPS 140
testing needs to be enabled in the same manner as it happened for
master and 7.x in elastic#48378 and elastic#49485

resolves: elastic#51924

Author: jkakavas

.ci/matrix-runtime-javas.yml

@@ -7,7 +7,6 @@
 
 ES_RUNTIME_JAVA:
   - java8
-  - java8fips
   - java11
   - java12
   - openjdk12