Change Default SPH (to actually work)

This MR:

• Changes the Default SPH implementation to actually compile and run tests, now using the ANARCHY viscosity switch and the PHANTOM SPH diffusion;
• Removes two unused tests testSingle.c and testSPHStep.c that were always only activated in the case of DEFAULT_SPH that did not work,

src/hydro/AnarchyDU/hydro_iact.h

 /*******************************************************************************
- * This file is part* of SWIFT.
+ * This file is part of SWIFT.
  * Coypright (c) 2019 Josh Borrow (joshua.borrow@durham.ac.uk) &
  *                    Matthieu Schaller (matthieu.schaller@durham.ac.uk)
  *
@@ -33,10 +33,10 @@
 #include "./hydro_parameters.h"
 
 /**
- * @brief Density interaction between two part*icles.
+ * @brief Density interaction between two particles.
  *
- * @param r2 Comoving square distance between the two part*icles.
- * @param dx Comoving vector separating both part*icles (pi - pj).
+ * @param r2 Comoving square distance between the two particles.
+ * @param dx Comoving vector separating both particles (pi - pj).
  * @param hi Comoving smoothing-length of part*icle i.
  * @param hj Comoving smoothing-length of part*icle j.
  * @param pi First part*icle.
@@ -109,10 +109,10 @@ __attribute__((always_inline)) INLINE static void runner_iact_density(
 }
 
 /**
- * @brief Density interaction between two part*icles (non-symmetric).
+ * @brief Density interaction between two particles (non-symmetric).
  *
- * @param r2 Comoving square distance between the two part*icles.
- * @param dx Comoving vector separating both part*icles (pi - pj).
+ * @param r2 Comoving square distance between the two particles.
+ * @param dx Comoving vector separating both particles (pi - pj).
  * @param hi Comoving smoothing-length of part*icle i.
  * @param hj Comoving smoothing-length of part*icle j.
  * @param pi First part*icle.
@@ -292,10 +292,10 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_gradient(
 }
 
 /**
- * @brief Force interaction between two part*icles.
+ * @brief Force interaction between two particles.
  *
- * @param r2 Comoving square distance between the two part*icles.
- * @param dx Comoving vector separating both part*icles (pi - pj).
+ * @param r2 Comoving square distance between the two particles.
+ * @param dx Comoving vector separating both particles (pi - pj).
  * @param hi Comoving smoothing-length of part*icle i.
  * @param hj Comoving smoothing-length of part*icle j.
  * @param pi First part*icle.
@@ -418,10 +418,10 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
 }
 
 /**
- * @brief Force interaction between two part*icles (non-symmetric).
+ * @brief Force interaction between two particles (non-symmetric).
  *
- * @param r2 Comoving square distance between the two part*icles.
- * @param dx Comoving vector separating both part*icles (pi - pj).
+ * @param r2 Comoving square distance between the two particles.
+ * @param dx Comoving vector separating both particles (pi - pj).
  * @param hi Comoving smoothing-length of part*icle i.
  * @param hj Comoving smoothing-length of part*icle j.
  * @param pi First part*icle.
@@ -538,8 +538,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
 /**
  * @brief Timestep limiter loop
  *
- * @param r2 Comoving square distance between the two part*icles.
- * @param dx Comoving vector separating both part*icles (pi - pj).
+ * @param r2 Comoving square distance between the two particles.
+ * @param dx Comoving vector separating both particles (pi - pj).
  * @param hi Comoving smoothing-length of part*icle i.
  * @param hj Comoving smoothing-length of part*icle j.
  * @param pi First part*icle.
@@ -558,8 +558,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_limiter(
 /**
  * @brief Timestep limiter loop (non-symmetric version)
  *
- * @param r2 Comoving square distance between the two part*icles.
- * @param dx Comoving vector separating both part*icles (pi - pj).
+ * @param r2 Comoving square distance between the two particles.
+ * @param dx Comoving vector separating both particles (pi - pj).
  * @param hi Comoving smoothing-length of part*icle i.
  * @param hj Comoving smoothing-length of part*icle j.
  * @param pi First part*icle.