Remove boehm gc patch for android tkill

Mono's Boehm GC was replaced with a newer one on latest versions, and the new
one already has this patch.

This change won't be a problem for older versions as we don't build boehm anyway.

files/patches/fix-mono-android-tkill.diff

@@ -1,35 +1,3 @@
-diff --git a/libgc/include/private/gcconfig.h b/libgc/include/private/gcconfig.h
-index e2bdf13ac3e..f962200ba4e 100644
---- a/libgc/include/private/gcconfig.h
-+++ b/libgc/include/private/gcconfig.h
-@@ -2255,6 +2255,14 @@
- #   define GETPAGESIZE() getpagesize()
- # endif
- 
-+#if defined(HOST_ANDROID) && !(__ANDROID_API__ >= 23) \
-+    && ((defined(MIPS) && (CPP_WORDSZ == 32)) \
-+        || defined(ARM32) || defined(I386) /* but not x32 */)
-+  /* tkill() exists only on arm32/mips(32)/x86. */
-+  /* NDK r11+ deprecates tkill() but keeps it for Mono clients. */
-+# define USE_TKILL_ON_ANDROID
-+#endif
-+
- # if defined(SUNOS5) || defined(DRSNX) || defined(UTS4)
- 	    /* OS has SVR4 generic features.  Probably others also qualify.	*/
- #   define SVR4
-diff --git a/libgc/pthread_stop_world.c b/libgc/pthread_stop_world.c
-index f93ce26b562..4a49a6d578c 100644
---- a/libgc/pthread_stop_world.c
-+++ b/libgc/pthread_stop_world.c
-@@ -336,7 +336,7 @@ void GC_push_all_stacks()
- pthread_t GC_stopping_thread;
- int GC_stopping_pid;
- 
--#ifdef HOST_ANDROID
-+#ifdef USE_TKILL_ON_ANDROID
- static
- int android_thread_kill(pid_t tid, int sig)
- {
 diff --git a/mono/metadata/threads.c b/mono/metadata/threads.c
 index ad9b8823f8f..3542b32b540 100644
 --- a/mono/metadata/threads.c