Remove redundancy

As DEBIAN_FRONTEND has been set as environment variable, there is no need to use DEBIAN_FRONTEND=noninteractive inside RUN lines, it is redundant, hence it has been removed.

ci-scripts/docker/Dockerfile.cppcheck.xenial

@@ -30,8 +30,8 @@ FROM ubuntu:xenial AS oai-cppcheck
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update && \
-    DEBIAN_FRONTEND=noninteractive apt-get upgrade --yes && \
-    DEBIAN_FRONTEND=noninteractive apt-get install --yes \
+    apt-get upgrade --yes && \
+    apt-get install --yes \
        build-essential \
        vim \
        cppcheck

ci-scripts/docker/Dockerfile.formatting.ubuntu24

@@ -33,8 +33,8 @@ ARG TARGET_BRANCH
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update && \
-    DEBIAN_FRONTEND=noninteractive apt-get upgrade --yes && \
-    DEBIAN_FRONTEND=noninteractive apt-get install --yes \
+    apt-get upgrade --yes && \
+    apt-get install --yes \
        gawk \
        git