[skip ci] not needed anymore

installation/patch/fwbw_derivative

@@ -1,13 +0,0 @@
-diff --git a/code/numerics.f90 b/code/numerics.f90
-index 24bd190..c968c70 100644
---- a/code/numerics.f90
-+++ b/code/numerics.f90
-@@ -110,7 +110,7 @@ module numerics
-    fftw_plan_mode             = 'FFTW_PATIENT'                                                      !< reads the planing-rigor flag, see manual on www.fftw.org, Default FFTW_PATIENT: use patient planner flag
-  character(len=64), protected, public :: & 
-    spectral_solver            = 'basicpetsc'  , &                                                   !< spectral solution method 
--   spectral_derivative        = 'continuous'                                                        !< spectral spatial derivative method
-+   spectral_derivative        = 'fwbw_difference'                                                   !< spectral spatial derivative method
-  character(len=1024), protected, public :: &
-    petsc_defaultOptions       = '-mech_snes_type ngmres &
-                                 &-damage_snes_type ngmres &