Remove unused update flag

Author: filipopo

docker/Dockerfile

@@ -7,7 +7,7 @@ ARG PPA_VARIANT
 
 # workaround interractive prompts during apt installations and install the MRS UAV System
 RUN echo 'debconf debconf/frontend select Noninteractive' | sudo debconf-set-selections && \
-    apt-get -y update && curl https://ctu-mrs.github.io/ppa2-${PPA_VARIANT}/add_ppa.sh | bash && \
+    apt-get update && curl https://ctu-mrs.github.io/ppa2-${PPA_VARIANT}/add_ppa.sh | bash && \
     apt-get --no-install-recommends -y install ros-jazzy-mrs-uav-system-full \
     ros-jazzy-mavros-extras gdb keyboard-configuration software-properties-common && \
     apt-get clean && rm -rf /var/lib/apt/lists/*