fix doc to remove default and include Dave's suggestion

Docs/source/usage/parameters.rst

@@ -1377,10 +1377,10 @@ External fields
 Grid initialization
 ^^^^^^^^^^^^^^^^^^^
 
-* ``warpx.B_ext_grid_init_style`` (string) optional (default is "default")
+* ``warpx.B_ext_grid_init_style`` (string) optional
     This parameter determines the type of initialization for the external
-    magnetic field. The "default" style initializes the
-    external magnetic field (Bx,By,Bz) to (0.0, 0.0, 0.0).
+    magnetic field. By default, the
+    external magnetic field (Bx,By,Bz) is initialized to (0.0, 0.0, 0.0).
     The string can be set to "constant" if a constant magnetic field is
     required to be set at initialization. If set to "constant", then an
     additional parameter, namely, ``warpx.B_external_grid`` must be specified.
@@ -1408,9 +1408,9 @@ Grid initialization
     Regarding how to prepare the openPMD data file, one can refer to
     the `openPMD-example-datasets <https://github.com/openPMD/openPMD-example-datasets>`__.
 
-* ``warpx.E_ext_grid_init_style`` (string) optional (default is "default")
+* ``warpx.E_ext_grid_init_style`` (string) optional
     This parameter determines the type of initialization for the external
-    electric field. The "default" style initializes the
+    electric field. By default, the
     external electric field (Ex,Ey,Ez) to (0.0, 0.0, 0.0).
     The string can be set to "constant" if a constant electric field is
     required to be set at initialization. If set to "constant", then an
@@ -1453,12 +1453,9 @@ Grid initialization
     than periodic.
 
 * ``warpx.maxlevel_extEMfield_init`` (default is maximum number of levels in the simulation)
-    With this parameter, the externally applied electric and magnetic fields with parameters
-    ``warpx.E_ext_grid_init_style="constant"``,
-    ``warpx.B_ext_grid_init_style="constant"``,
-    ``warpx.E_ext_grid_init_style="parse_E_ext_grid_function"`` and
-    ``warpx.B_ext_grid_init_style="parse_B_ext_grid_function"`` will not be initialized with the external field
-    for levels strictly greater than ``warpx.maxlevel_extEMfield_init``. For some mesh-refinement simulations,
+    With this parameter, the externally applied electric and magnetic fields
+    will not be applied for levels greater than ``warpx.maxlevel_extEMfield_init``.
+    For some mesh-refinement simulations,
     the external fields are only applied to the parent grid and not the refined patches. In such cases,
     ``warpx.maxlevel_extEMfield_init`` can be set to 0. Note that the other levels will be initialized to
     a default value of 0.