WarpX: master is the new develop (#14898)

WarpX removed the `dev` branch in favor of a simpler,
`master`-centric development model.
`master` is the new development branch and there is no
stable branch anymore (we use tags and release branches
instead).

var/spack/repos/builtin/packages/warpx/package.py

@@ -18,8 +18,9 @@ class Warpx(MakefilePackage):
     homepage = "https://ecp-warpx.github.io/index.html"
     git      = "https://github.com/ECP-WarpX/WarpX.git"
 
+    maintainers = ['ax3l', 'dpgrote', 'MaxThevenet', 'RemiLehe']
+
     version('master', tag='master')
-    version('dev', tag='dev')
 
     depends_on('mpi')
 
@@ -40,11 +41,6 @@ class Warpx(MakefilePackage):
     resource(name='amrex',
              git='https://github.com/AMReX-Codes/amrex.git',
              when='@master',
-             tag='master')
-
-    resource(name='amrex',
-             git='https://github.com/AMReX-Codes/amrex.git',
-             when='@dev',
              tag='development')
 
     resource(name='picsar',