packaging: disable rust extensions again on CentOS

Backed out changeset eccbfa7e19c0
We're seeing (very rarely) crashes of 'hg purge' on some of our machines
(see https://bz.mercurial-scm.org/show_bug.cgi?id=6509 ).
Unfortunately, I haven't been able to find out much more about
what is going wrong.
To avoid further impact on our users and CI,
I would prefer to disable the rust extensions for now.

Differential Revision: https://phab.mercurial-scm.org/D10877

contrib/packaging/docker/centos7

@@ -15,6 +15,3 b' RUN yum install -y \\'
 
 # For creating repo meta data
 RUN yum install -y createrepo
-
-# For rust extensions
-RUN yum install -y cargo

contrib/packaging/docker/centos8

@@ -13,6 +13,3 b' RUN yum install -y \\'
 
 # For creating repo meta data
 RUN yum install -y createrepo
-
-# For rust extensions
-RUN yum install -y cargo

contrib/packaging/mercurial.spec

@@ -110,14 +110,14 b' cd %{docutilsname}'
 LD_LIBRARY_PATH=$PYPATH $PYPATH/python setup.py install --root="$RPM_BUILD_ROOT"
 cd -
 
-PATH=$PYPATH:$PATH LD_LIBRARY_PATH=$PYPATH make install PYTHON=%{pythonexe} DESTDIR=$RPM_BUILD_ROOT PREFIX=%{hgpyprefix} MANDIR=%{_mandir} PURE="--rust"
+PATH=$PYPATH:$PATH LD_LIBRARY_PATH=$PYPATH make install PYTHON=%{pythonexe} DESTDIR=$RPM_BUILD_ROOT PREFIX=%{hgpyprefix} MANDIR=%{_mandir}
 mkdir -p $RPM_BUILD_ROOT%{_bindir}
 ( cd $RPM_BUILD_ROOT%{_bindir}/ && ln -s ../..%{hgpyprefix}/bin/hg . )
 ( cd $RPM_BUILD_ROOT%{_bindir}/ && ln -s ../..%{hgpyprefix}/bin/python2.? %{pythonhg} )
 
 %else
 
-make install PYTHON=%{pythonexe} DESTDIR=$RPM_BUILD_ROOT PREFIX=%{_prefix} MANDIR=%{_mandir} PURE="--rust"
+make install PYTHON=%{pythonexe} DESTDIR=$RPM_BUILD_ROOT PREFIX=%{_prefix} MANDIR=%{_mandir}
 
 %endif