tf-a: remove clang-tools-6.0 duplicate

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>
Change-Id: If0f3dc3544cd556b80b398b9c79f1c376c5d849b
diff --git a/bionic-amd64-tf-a-build/Dockerfile b/bionic-amd64-tf-a-build/Dockerfile
index 6307b0f..e0d1583 100644
--- a/bionic-amd64-tf-a-build/Dockerfile
+++ b/bionic-amd64-tf-a-build/Dockerfile
@@ -11,7 +11,6 @@
     build-essential \
     clang-tools-6.0 \
     curl \
-    clang-tools-6.0 \
     default-jre \
     device-tree-compiler \
     doxygen \