doc/general: remove 8SVX audio, there is no such codec

While here add missing PCM signed 8-bit planar.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/general.texi

@@ -715,7 +715,6 @@ following image formats are supported:
 
 @multitable @columnfractions .4 .1 .1 .4
 @item Name @tab Encoding @tab Decoding @tab Comments
-@item 8SVX audio             @tab     @tab  X
 @item 8SVX exponential       @tab     @tab  X
 @item 8SVX fibonacci         @tab     @tab  X
 @item AAC+                   @tab  E  @tab  X
@@ -828,6 +827,7 @@ following image formats are supported:
     @tab supported through external library libopus
 @item PCM A-law              @tab  X  @tab  X
 @item PCM mu-law             @tab  X  @tab  X
+@item PCM signed 8-bit planar  @tab     @tab  X
 @item PCM signed 16-bit big-endian planar  @tab     @tab  X
 @item PCM signed 16-bit little-endian planar  @tab     @tab  X
 @item PCM signed 24-bit little-endian planar  @tab     @tab  X