vendor/botan: Remove

This is infrequently maintained, and has been a strict subset of what is
available in `core:crypto` for a while.  Instead of improving the
bindings, it is better to spend resources improving `core:crypto`.

tests/vendor/build.bat

@@ -1,13 +1,8 @@
-@echo off
-set COMMON=-show-timings -no-bounds-check -vet -strict-style
-set PATH_TO_ODIN==..\..\odin
-
-echo ---
-echo Running vendor:botan tests
-echo ---
-%PATH_TO_ODIN% run botan %COMMON% -out:vendor_botan.exe || exit /b
-
-echo ---
-echo Running vendor:glfw tests
-echo ---
+@echo off
+set COMMON=-show-timings -no-bounds-check -vet -strict-style
+set PATH_TO_ODIN==..\..\odin
+
+echo ---
+echo Running vendor:glfw tests
+echo ---
 %PATH_TO_ODIN% run glfw %COMMON% -out:vendor_glfw.exe || exit /b