Fix 🩹 (almost) all warnings ⚠️ with default configuration (DIM=3, openMP+MPI, double precision, no advanced solvers, no QED, native output) (#1263)

This PR should fix almost all the compilation warnings in the default configuration (DIM=3, openMP+MPI, double precision, no advanced solvers, no QED, native output...). Or at least it does that on my system (my compiler is `g++ (Ubuntu 9.3.0-10ubuntu2) 9.3.0` ).

I have just two residual warnings:

### 1
```
[ 89%] Building CXX object CMakeFiles/WarpX.dir/Source/Parser/wp_parser.lex.cpp.o
wp_parser.lex.c:1356:17: warning: ‘void yyunput(int, char*)’ defined but not used [-Wunused-function]
```
I don't know if `yyunput(int, char*)` is there for a reason, even if it is not used. So I didn't do anything.


### 2
```
[ 96%] Building CXX object CMakeFiles/WarpX.dir/Source/Utils/CoarsenIO.cpp.o
/home/luca/Projects/warpx_dir/WarpX/Source/Particles/WarpXParticleContainer.cpp: In member function ‘void WarpXParticleContainer::AddNParticles(int, int, const ParticleReal*, const ParticleReal*, const ParticleReal*, const ParticleReal*, const ParticleReal*, const ParticleReal*, int, const ParticleReal*, int, int)’:
/home/luca/Projects/warpx_dir/WarpX/Source/Particles/WarpXParticleContainer.cpp:102:44: warning: unused parameter ‘nattr’ [-Wunused-parameter]
  102 |                                        int nattr, const ParticleReal* attr, int uniqueparticles, int id)
```
The first line of `AddNParticles` is `BL_ASSERT(nattr == 1); //! @fixme nattr is unused below: false sense of safety` . So I thought that there might be something to fix here and I didn't do anything.

1 files changed, 0 insertions, 1 deletions

diff --git a/Source/Particles/RigidInjectedParticleContainer.cpp b/Source/Particles/RigidInjectedParticleContainer.cpp
index 1a480aae7..8b8237ceb 100644
--- a/Source/Particles/RigidInjectedParticleContainer.cpp
+++ b/Source/Particles/RigidInjectedParticleContainer.cpp
@@ -410,7 +410,6 @@ RigidInjectedParticleContainer::PushP (int lev, Real dt,
             const FArrayBox& bzfab = Bz[pti];
 
             const auto getPosition = GetParticlePosition(pti);
-                  auto setPosition = SetParticlePosition(pti);
 
             const auto getExternalE = GetExternalEField(pti);
             const auto getExternalB = GetExternalBField(pti);