input: disable gamepad code by default

Enabling this by default probably causes a number of issues, such as
breaking vo_sdl, or reacting to various input devices while the window
is not focused. It's also pretty obscure, or at least new. Disable it by
default.

DOCS/man/options.rst

@@ -3408,7 +3408,7 @@ Input
     Enable/disable Apple Remote support. Enabled by default (except for libmpv).
 
 ``--input-gamepad=<yes|no>``
-    Enable/disable SDL2 Gamepad support. Enabled by default (except for libmpv).
+    Enable/disable SDL2 Gamepad support. Disabled by default.
 
 ``--input-cursor``, ``--no-input-cursor``
     Permit mpv to receive pointer events reported by the video output

etc/builtin.conf

@@ -26,7 +26,6 @@ input-terminal=no
 osc=no
 input-default-bindings=no
 input-vo-keyboard=no
-input-gamepad=no
 # OSX/Cocoa global input hooks
 input-appleremote=no
 input-media-keys=no

input/input.c

@@ -218,9 +218,6 @@ const struct m_sub_options input_config = {
         .use_media_keys = 1,
 #if HAVE_COCOA
         .use_appleremote = 1,
-#endif
-#if HAVE_SDL2_GAMEPAD
-        .use_gamepad = 1,
 #endif
         .default_bindings = 1,
         .vo_key_input = 1,