all: remove support for stage1

With almost all tests/examples working on all platforms now with the new compiler,
hexops/mach#180, it's time to remove stage1 support.

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/opengl.zig

@@ -153,7 +153,7 @@ const builtin = @import("builtin");
 /// Generic function pointer used for returning client API function pointers.
 ///
 /// see also: context_glext, glfwGetProcAddress
-pub const GLProc = if (builtin.zig_backend == .stage1 or builtin.zig_backend == .other) fn () callconv(.C) void else *const fn () callconv(.C) void;
+pub const GLProc = *const fn () callconv(.C) void;
 
 /// Returns the address of the specified function for the current context.
 ///

src/vulkan.zig

@@ -34,10 +34,7 @@ pub fn initVulkanLoader(loader_function: ?VKGetInstanceProcAddr) void {
     c.glfwInitVulkanLoader(loader_function orelse null);
 }
 
-pub const VKGetInstanceProcAddr = if (@import("builtin").zig_backend == .stage1)
-    fn (vk_instance: c.VkInstance, name: [*c]const u8) callconv(.C) ?VKProc
-else
-    *const fn (vk_instance: c.VkInstance, name: [*c]const u8) callconv(.C) ?VKProc;
+pub const VKGetInstanceProcAddr = *const fn (vk_instance: c.VkInstance, name: [*c]const u8) callconv(.C) ?VKProc;
 
 /// Returns whether the Vulkan loader and an ICD have been found.
 ///
@@ -106,10 +103,7 @@ pub inline fn getRequiredInstanceExtensions() error{APIUnavailable}![][*:0]const
 /// Generic function pointer used for returning Vulkan API function pointers.
 ///
 /// see also: vulkan_proc, glfw.getInstanceProcAddress
-pub const VKProc = if (@import("builtin").zig_backend == .stage1)
-    fn () callconv(.C) void
-else
-    *const fn () callconv(.C) void;
+pub const VKProc = *const fn () callconv(.C) void;
 
 /// Returns the address of the specified Vulkan instance function.
 ///