[build] remove examples/build.zig, incorporate into main build.zig

Removes the second build.zig in the examples directory and incorporates it
into the main build.zig. This gives the zig build system the data needed to
know if the raylib library needs to be rebuilt when running any example.

build.zig.zon

@@ -22,5 +22,6 @@
         "build.zig",
         "build.zig.zon",
         "src",
+        "examples",
     },
 }