Revert "Added -j option to dpkg-buildpackage to speed up build"

This reverts commit a89a6e4f.

We cannot blindly assume all CPUs on all hosts are available for
building. For example our own buildbot.mariadb.org builders go
amok if everey host CPU core is used in parallel for every build
on a host.

This option should be configurable, and in fact it already is via
the parallel=N setting in DEB_BUILD_OPTIONS. See debian/rules
for details.

debian/autobake-deb.sh

@@ -160,7 +160,7 @@ fi
 # Build the package
 # Pass -I so that .git and other unnecessary temporary and source control files
 # will be ignored by dpkg-source when creating the tar.gz source package.
-fakeroot dpkg-buildpackage -us -uc -I $BUILDPACKAGE_FLAGS -j$(nproc)
+fakeroot dpkg-buildpackage -us -uc -I $BUILDPACKAGE_FLAGS
 
 # If the step above fails due to missing dependencies, you can manually run
 #   sudo mk-build-deps debian/control -r -i