Bug#897752: freefem3d: ftbfs with GCC-8

[Rebecca N. Palmer]

Control: tags -1 patch

The error is

In file included from FatBoundary.cpp:25:
./FEMDiscretization.hpp:647:7: error: too many template-parameter-lists
  class FEMDiscretization<Structured3DMesh,TypeOfDiscretization>
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix:

Description: Use correct syntax for partial template specialization

This is probably unused (the use in FatBoundary is commented out),
which would explain it only being an FTBFS in GCC 8 and not sooner:
https://gcc.gnu.org/gcc-8/porting_to.html#hypothetical-instantiation

Author: Rebecca N. Palmer <rebecca_palmer at zoho.com>
Bug-Debian: https://bugs.debian.org/897752
Forwarded: no

--- a/solver/FEMDiscretization.hpp
+++ b/solver/FEMDiscretization.hpp
@@ -642,7 +642,6 @@ public:
   * It is an important specialization since the elementary matrices are
   * computed \b once for all!
   */
-template <>
  template <DiscretizationType::Type TypeOfDiscretization>
  class FEMDiscretization<Structured3DMesh,TypeOfDiscretization>
    : public BaseFEMDiscretization<Structured3DMesh,