fix: apt error after imap installed (#2212)

php-fpm/Dockerfile

@@ -573,7 +573,6 @@ ARG INSTALL_IMAP=false
 
 RUN if [ ${INSTALL_IMAP} = true ]; then \
     apt-get install -y libc-client-dev libkrb5-dev && \
-    rm -r /var/lib/apt/lists/* && \
     docker-php-ext-configure imap --with-kerberos --with-imap-ssl && \
     docker-php-ext-install imap \
 ;fi