Remove apt lists after 'apt-get update' in docker-contributor/Dockerfile

We already do this in all other places. It reduces the size of the
image.

(Note that the 'rm' command has to be done in the same RUN instruction
as 'apt-get update', otherwise the lists will still be stored in the
intermediate layers. So some of the RUN instructions had to be
merged.)

docker-contributor/Dockerfile

@@ -57,13 +57,13 @@ RUN php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" &&
     && mv /composer.phar /usr/local/bin/composer
 
 # Install all supported PHP versions
-RUN add-apt-repository ppa:ondrej/php -y && apt-get update
-RUN for VERSION in $PHPSUPPORTED; do \
+RUN add-apt-repository ppa:ondrej/php -y && apt-get update && \
+    for VERSION in $PHPSUPPORTED; do \
         if [ "${VERSION}" != "8.3" ]; then \
             $APTINSTALL php${VERSION}; \
         fi; \
-    done
-RUN PACKAGES=$(dpkg-query -f '${binary:Package}\n' -W|grep "^php.*-"); \
+    done && \
+    PACKAGES=$(dpkg-query -f '${binary:Package}\n' -W|grep "^php.*-") && \
     for PACKAGE in $PACKAGES; do \
         PACKAGEALLVERSIONS="" && \
         for VERSION in $PHPSUPPORTED; do \
@@ -72,8 +72,9 @@ RUN PACKAGES=$(dpkg-query -f '${binary:Package}\n' -W|grep "^php.*-"); \
             fi; \
         done; \
         $APTINSTALL $PACKAGEALLVERSIONS; \
-    done
-RUN update-alternatives --set php /usr/bin/php${DEFAULTPHPVERSION}
+    done && \
+    update-alternatives --set php /usr/bin/php${DEFAULTPHPVERSION} && \
+    rm -rf /var/lib/apt/lists/*
 
 # Set up alternatives for PHP-FPM
 RUN for VERSION in $PHPSUPPORTED; do \
@@ -88,7 +89,7 @@ COPY ["php-config", "/php-config"]
 RUN for VERSION in $PHPSUPPORTED; do \
         cp -Rf /php-config/* /etc/php/${VERSION}/cli/conf.d; \
         cp -Rf /php-config/* /etc/php/${VERSION}/fpm/conf.d; \
-    done; \ 
+    done; \
     rm -Rf /php-config
 
 # Disable Xdebug by default