Remove some old BeOS artefacts

- checking for beos systems is no longer relevant in configure.ac
- usage of undefined constant BETHREADS removed.

Closes GH-4346

Author: petk

TSRM/TSRM.h

@@ -52,9 +52,6 @@ typedef uintptr_t tsrm_uintptr_t;
 # include <pthread.h>
 #elif defined(TSRM_ST)
 # include <st.h>
-#elif defined(BETHREADS)
-#include <kernel/OS.h>
-#include <TLS.h>
 #endif
 
 #if SIZEOF_SIZE_T == 4

configure.ac

@@ -282,10 +282,6 @@ case $host_alias in
     fi
     php_multiple_shlib_versions_ok=yes
     ;;
-  *beos*)
-    beos_threads=1
-    LIBS="$LIBS -lbe -lroot"
-    ;;
   *mips*)
     CPPFLAGS="$CPPFLAGS -D_XPG_IV"
     ;;