vo_opengl: remove non-working rgb/rgba FBO formats

Following commit 84ccebd9, the internal helpers don't allow GL_RGB and
GL_RGBA as internal formats for FBO attachments anymore.

While OpenGL itself is perfectly fine with it, I don't see much of a
reason to bother, and mixing sized and unsized internal formats is
confusing anyway.

Just remove these formats.

DOCS/interface-changes.rst

@@ -32,6 +32,8 @@ Interface changes
       as booleans when using the mpv_node functions in the client API, the
       "native" property accessors in Lua, and the JSON API. They can be set as
       such as well.
+    - the VO opengl fbo-format sub-option does not accept "rgb" or "rgba"
+      anymore
  --- mpv 0.17.0 ---
     - deprecate "track-list/N/audio-channels" property (use
       "track-list/N/demux-channel-count" instead)

DOCS/man/vo.rst

@@ -974,7 +974,7 @@ Available video output drivers are:
     ``fbo-format=<fmt>``
         Selects the internal format of textures used for FBOs. The format can
         influence performance and quality of the video output.
-        ``fmt`` can be one of: rgb, rgba, rgb8, rgb10, rgb10_a2, rgb16, rgb16f,
+        ``fmt`` can be one of: rgb8, rgb10, rgb10_a2, rgb16, rgb16f,
         rgb32f, rgba12, rgba16, rgba16f, rgba32f.
         Default: ``auto``, which maps to rgba16 on desktop GL, and rgba16f or
         rgb10_a2 on GLES (e.g. ANGLE), unless GL_EXT_texture_norm16 is

video/out/opengl/video.c

@@ -401,9 +401,7 @@ const struct m_sub_options gl_video_conf = {
         OPT_FLOATRANGE("sigmoid-center", sigmoid_center, 0, 0.0, 1.0),
         OPT_FLOATRANGE("sigmoid-slope", sigmoid_slope, 0, 1.0, 20.0),
         OPT_CHOICE("fbo-format", fbo_format, 0,
-                   ({"rgb",    GL_RGB},
-                    {"rgba",   GL_RGBA},
-                    {"rgb8",   GL_RGB8},
+                   ({"rgb8",   GL_RGB8},
                     {"rgba8",  GL_RGBA8},
                     {"rgb10",  GL_RGB10},
                     {"rgb10_a2", GL_RGB10_A2},