Removed -s / --save_last_frame flag from CLI arguments (#3528)

* Remove -s flag

* Make help text more verbose

Author: gixtox

manim/cli/render/render_options.py

@@ -59,7 +59,13 @@ def validate_resolution(ctx, param, value):
         type=Choice(["png", "gif", "mp4", "webm", "mov"], case_sensitive=False),
         default=None,
     ),
-    option("-s", "--save_last_frame", is_flag=True, default=None),
+    option(
+        "-s",
+        "--save_last_frame",
+        default=None,
+        is_flag=True,
+        help="Render and save only the last frame of a scene as a PNG image.",
+    ),
     option(
         "-q",
         "--quality",
@@ -123,13 +129,6 @@ def validate_resolution(ctx, param, value):
         is_flag=True,
         help="Save section videos in addition to movie file.",
     ),
-    option(
-        "-s",
-        "--save_last_frame",
-        default=None,
-        is_flag=True,
-        help="Save last frame as png (Deprecated).",
-    ),
     option(
         "-t",
         "--transparent",