[colm] obsolete alloca.h header

[Peter Reijnders]

Hello

While compiling colm on netbsd 7.0.2 I found that there is one obsolete
include. Without this line colm compiles and seems to run.

Peter Reijnders

```
diff --git a/src/program.c b/src/program.c
index 0002ae5..0d80677 100644
--- a/src/program.c
+++ b/src/program.c
@@ -20,7 +20,6 @@
  * SOFTWARE.
  */
 
-#include <alloca.h>
 #include <sys/mman.h>
 #include <string.h>
 #include <assert.h>
```