Update Golang image for Buster

Buster provides clang-7.0

golang/latest/Dockerfile

@@ -9,28 +9,13 @@ ENV GOPATH /go
 ENV PATH ${GOPATH}/bin:$PATH
 RUN go get -u golang.org/x/lint/golint
 
-# Install requirement to import LLVM key
+# Install clang
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    gnupg2 \
-    wget \
-    && apt-get clean \
-    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
-
-# Add apt key for LLVM repository
-SHELL ["/bin/bash", "-o", "pipefail", "-c"]
-RUN wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
-
-# Add LLVM apt repository
-SHELL ["/bin/bash", "-o", "pipefail", "-c"]
-RUN echo "deb http://apt.llvm.org/stretch/ llvm-toolchain-stretch-5.0 main" | tee -a /etc/apt/sources.list
-
-# Install clang from LLVM repository
-RUN apt-get update && apt-get install -y --no-install-recommends \
-    clang-5.0 \
+    clang-7.0 \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 # Set Clang as default CC
 ENV set_clang /etc/profile.d/set-clang-cc.sh
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
-RUN echo "export CC=clang-5.0" | tee -a ${set_clang} && chmod a+x ${set_clang}
+RUN echo "export CC=clang-7.0" | tee -a ${set_clang} && chmod a+x ${set_clang}