avfilter/fps: remove unconventional acronyms

In dd770883e9, support for expressions was added. Among the constants
added were labels of qnstc, qpal, sntsc & spal.

These were added in ba2a8cb40b to represent parameter permutations where
only the resolution is different. They don't have any usage currency and
don't represent any industry standards or convention in terms of framerate.

doc/filters.texi

@@ -12341,10 +12341,10 @@ constants:
 @item source_fps
 The input's frame rate
 
-@item ntsc, qntsc, sntsc
+@item ntsc
 NTSC frame rate of @code{30000/1001}
 
-@item pal, qpal, spal
+@item pal
 PAL frame rate of @code{25.0}
 
 @item film

libavfilter/vf_fps.c

@@ -47,10 +47,6 @@ static const char *const var_names[] = {
   "source_fps",
   "ntsc",
   "pal",
-  "qntsc",
-  "qpal",
-  "sntsc",
-  "spal",
   "film",
   "ntsc_film",
   NULL
@@ -60,10 +56,6 @@ enum var_name {
   VAR_SOURCE_FPS,
   VAR_FPS_NTSC,
   VAR_FPS_PAL,
-  VAR_FPS_QNTSC,
-  VAR_FPS_QPAL,
-  VAR_FPS_SNTSC,
-  VAR_FPS_SPAL,
   VAR_FPS_FILM,
   VAR_FPS_NTSC_FILM,
   VARS_NB
@@ -71,10 +63,6 @@ enum var_name {
 
 static const double ntsc_fps = 30000.0 / 1001.0;
 static const double pal_fps = 25.0;
-static const double qntsc_fps = 30000.0 / 1001.0;
-static const double qpal_fps = 25.0;
-static const double sntsc_fps = 30000.0 / 1001.0;
-static const double spal_fps = 25.0;
 static const double film_fps = 24.0;
 static const double ntsc_film_fps = 24000.0 / 1001.0;
 
@@ -194,10 +182,6 @@ static int config_props(AVFilterLink* outlink)
     var_values[VAR_SOURCE_FPS]    = av_q2d(inlink->frame_rate);
     var_values[VAR_FPS_NTSC]      = ntsc_fps;
     var_values[VAR_FPS_PAL]       = pal_fps;
-    var_values[VAR_FPS_QNTSC]     = qntsc_fps;
-    var_values[VAR_FPS_QPAL]      = qpal_fps;
-    var_values[VAR_FPS_SNTSC]     = sntsc_fps;
-    var_values[VAR_FPS_SPAL]      = spal_fps;
     var_values[VAR_FPS_FILM]      = film_fps;
     var_values[VAR_FPS_NTSC_FILM] = ntsc_film_fps;
     ret = av_expr_parse_and_eval(&res, s->framerate,