Revert "Make ex1.c and ex4.c be executable on any systems"

Using /usr/bin/env tcc doesn't work as it was reported.  Revert to
using the full path which fails if the user installs tcc in non-default
location.  Then again this is just an example.

This reverts commit 27a428cd0f.

examples/ex1.c

@@ -1,4 +1,4 @@
-#!/usr/bin/env tcc -run
+#!/usr/local/bin/tcc -run
 #include <tcclib.h>
 
 int main()

examples/ex4.c

@@ -1,4 +1,4 @@
-#!/usr/bin/env tcc -run -L/usr/X11R6/lib -lX11
+#!/usr/local/bin/tcc -run -L/usr/X11R6/lib -lX11
 #include <stdlib.h>
 #include <stdio.h>
 #include <X11/Xlib.h>