Revert "DO NOT MERGE"

This reverts commit 1f468153.

Notice that there are a few separate regtests for lepton

regtest/basic/rt-ghost-1/config

 type=driver
+plumed_needs="matheval"
 arg="--plumed plumed.dat --ixyz trajectory.xyz --dump-forces ff --dump-forces-fmt=%10.6f --dump-full-virial"
-export PLUMED_USE_LEPTON=yes

regtest/basic/rt-maxent-1/config

 type=driver
+plumed_needs="matheval"
 arg="--plumed plumed.dat --mf_xtc traj.xtc --dump-forces forces --dump-forces-fmt=%8.4f"
-export PLUMED_USE_LEPTON=yes

regtest/basic/rt-maxent-2/config

 type=driver
+plumed_needs="matheval"
 arg="--plumed plumed.dat --mf_xtc traj.xtc --dump-forces forces --dump-forces-fmt=%8.4f"
-export PLUMED_USE_LEPTON=yes
-

regtest/basic/rt-maxent-3/config

 mpiprocs=6
 type=driver
+plumed_needs="matheval"
 # this is to test a different name
 arg="--plumed plumed.dat --mf_xtc traj.xtc --dump-forces forces --multi 6 --dump-forces-fmt=%8.4f"
-export PLUMED_USE_LEPTON=yes
-

regtest/basic/rt-maxent-4/config

 mpiprocs=6
 type=driver
+plumed_needs="matheval"
 arg="--plumed plumed.dat --mf_xtc traj.xtc --dump-forces forces --dump-forces-fmt=%8.4f --debug-dd"
-export PLUMED_USE_LEPTON=yes

regtest/basic/rt-maxent-5/config

 mpiprocs=6
 type=driver
+plumed_needs="matheval"
 arg="--plumed plumed.dat --mf_xtc traj.xtc --dump-forces forces --multi 3 --dump-forces-fmt=%8.4f --debug-dd"
-export PLUMED_USE_LEPTON=yes

regtest/basic/rt23/config

 type=driver
 # this is to test a different name
 arg="--plumed plumed.dat --ixyz trajectory.xyz --dump-forces forces.xyz --dump-forces-fmt=%10.6f"
-export PLUMED_USE_LEPTON=yes
-
+plumed_needs="matheval"

regtest/basic/rt63c-mpi/config

 type=driver
 mpiprocs=2
+plumed_needs="matheval"
 arg="--plumed plumed.dat --trajectory-stride 10 --timestep 0.005 --igro helix.input.gro --dump-forces ff --dump-full-virial --dump-forces-fmt=%7.4f --debug-dd"
-export PLUMED_USE_LEPTON=yes

regtest/basic/rt63c/config

 type=driver
+plumed_needs="matheval"
 arg="--plumed plumed.dat --trajectory-stride 10 --timestep 0.005 --igro helix.input.gro --dump-forces ff --dump-full-virial --dump-forces-fmt=%7.4f"
-export PLUMED_USE_LEPTON=yes