remove unneeded extensions [PT #155688966]

Dockerfile

@@ -17,14 +17,7 @@ VOLUME /var/www/html/metadata
 
 # Install the gmp and mcrypt extensions
 RUN apt-get update -y && \
-    apt-get install -y git libgmp-dev re2c libmhash-dev libmcrypt-dev file && \
-    ln -s /usr/include/x86_64-linux-gnu/gmp.h /usr/local/include/ && \
-    docker-php-ext-configure gmp && \
-    docker-php-ext-install gmp && \
-    docker-php-ext-configure mcrypt && \
-    docker-php-ext-install mcrypt && \
-    echo extension=gmp.so > $PHP_INI_DIR/conf.d/gmp.ini && \
-    echo extension=mcrypt.so > $PHP_INI_DIR/conf.d/mcrypt.ini
+    apt-get install -y git re2c libmhash-dev file
 
 RUN curl -sS https://getcomposer.org/installer | php
 RUN php composer.phar install