Clean up forking and cloning.

The kernel now maintains the pthread_internal_t::tid field for us,
and __clone was only used in one place so let's inline it so we don't
have to leave such a dangerous function lying around. Also rename
files to match their content and remove some useless #includes.

Change-Id: I24299fb4a940e394de75f864ee36fdabbd9438f9
diff --git a/libc/Android.mk b/libc/Android.mk
index ab09089..551c633 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -77,7 +77,6 @@
 	bionic/atol.c \
 	bionic/atoll.c \
 	bionic/bindresvport.c \
-	bionic/bionic_clone.c \
 	bionic/clearenv.c \
 	bionic/daemon.c \
 	bionic/err.c \
@@ -207,6 +206,7 @@
     bionic/brk.cpp \
     bionic/chmod.cpp \
     bionic/chown.cpp \
+    bionic/clone.cpp \
     bionic/dirent.cpp \
     bionic/dup2.cpp \
     bionic/epoll_create.cpp \