distro/deb: don't explictly link agains libjemalloc

It seems that new versions of jemalloc (5.2) behave much worse than standard
libc malloc. The memory consumption only grows after huge AXFRs.

distro/deb/control

@@ -17,7 +17,6 @@ Build-Depends:
  libfstrm-dev,
  libgnutls28-dev,
  libidn2-0-dev,
- libjemalloc-dev,
  liblmdb-dev,
  libmaxminddb-dev [!powerpcspe !sh4 !x32],
  libnghttp2-dev,

distro/deb/rules

@@ -44,7 +44,6 @@ override_dh_auto_configure:
 	  --with-rundir=/run/knot \
 	  --with-moduledir=/usr/lib/$(DEB_HOST_MULTIARCH)/knot \
 	  --with-storage=/var/lib/knot \
-	  --with-memory-allocator=jemalloc \
 	  --enable-systemd=auto \
 	  --enable-dnstap \
 	  --with-module-dnstap=yes \