build: remove bogus client API examples build

The symlink trick made waf go crazy (deleting source files, getting
tangled up in infinite recursion... I wish I was joking). This means we
still can't build the client API examples in a reasonable way using the
include files of the local repository (instead of globally installed
headers). Not building them at all is better than deleting source files.

Instead, provide some manual instructions how to build each example
(except for the Qt examples, which provide qmake project files).

DOCS/client_api_examples/simple/simple.c

@@ -1,3 +1,5 @@
+// Build with: gcc -o simple simple.c `pkg-config --libs --cflags mpv`
+
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>