Removed `M_PI` variable

Fortran moules are public by default so limiting the number of
unecessary variables is important as to not populate the global scope.

api/GenApi.py

@@ -1403,7 +1403,6 @@ module gmsh
     integer, parameter :: {2}_API_VERSION_MINOR = {5}
     integer, parameter :: {2}_API_VERSION_PATCH = {6}
     character(len=100), parameter :: {2}_API_VERSION = "{4}.{5}.{6}"
-    real(c_double), parameter::M_PI = 3.14159265358979323846d0
 
     interface
 """

tutorials/fortran/t2.f90

@@ -98,7 +98,7 @@ program main
 
     call gmshModelGeoTranslate(t, 2_8, -0.02d0, 0d0, 0d0, ierr)
 
-    call gmshModelGeoRotate(t, 2_8, 0d0, 0.3d0, 0d0, 0d0, 0d0, 1d0, -M_PI / 4d0, ierr)
+    call gmshModelGeoRotate(t, 2_8, 0d0, 0.3d0, 0d0, 0d0, 0d0, 1d0, -acos(1.0) / 4d0, ierr)
 
     call gmshModelGeoCopy(iv, 2_8, ov, ov_n, ierr)