Remove numerous things deprecated during the 0.14 release cycle

Basically everything that has a direct replacement or no uses left.

Notable omissions:

- std.ArrayHashMap: Too much fallout, needs a separate cleanup.
- std.debug.runtime_safety: Too much fallout.
- std.heap.GeneralPurposeAllocator: Lots of references to it remain, not
  a simple find and replace as "debug allocator" is not equivalent to
  "general purpose allocator".
- std.io.Reader: Is being reworked at the moment.
- std.unicode.utf8Decode(): No replacement, needs a new API first.
- Manifest backwards compat options: Removal would break test data used
  by TestFetchBuilder.
- panic handler needs to be a namespace: Many tests still rely on it
  being a function, needs a separate cleanup.

doc/langref/build_c.zig

@@ -1,7 +1,8 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
-    const lib = b.addSharedLibrary(.{
+    const lib = b.addLibrary(.{
+        .linkage = .dynamic,
         .name = "mathtest",
         .root_source_file = b.path("mathtest.zig"),
         .version = .{ .major = 1, .minor = 0, .patch = 0 },

doc/langref/test_noreturn_from_exit.zig

@@ -3,7 +3,7 @@ const builtin = @import("builtin");
 const native_arch = builtin.cpu.arch;
 const expect = std.testing.expect;
 
-const WINAPI: std.builtin.CallingConvention = if (native_arch == .x86) .Stdcall else .C;
+const WINAPI: std.builtin.CallingConvention = if (native_arch == .x86) .{ .x86_stdcall = .{} } else .c;
 extern "kernel32" fn ExitProcess(exit_code: c_uint) callconv(WINAPI) noreturn;
 
 test "foo" {