Help: Generalize release note filename for add_custom_command DEPFILE

Rename the note added by commit d67cc4882d (Xcode: Add support of
DEPFILE for add_custom_command, 2021-04-15) to be more general.

Help/release/dev/Xcode-add_custom_command-DEPFILE.rst

@@ -1,5 +0,0 @@
-Xcode-add_custom_command-DEPFILE
---------------------------------
-
-* The :command:`add_custom_command` command gained ``DEPFILE`` support on
-  :generator:`Xcode` generator.

Help/release/dev/add_custom_command-DEPFILE.rst

@@ -0,0 +1,5 @@
+add_custom_command-DEPFILE
+--------------------------
+
+* The :command:`add_custom_command` command gained ``DEPFILE`` support on
+  the :generator:`Xcode` generator.