uapi headers: simplify the <linux/compiler.h> stuff.

We don't really need <linux/compiler.h> and <linux/compiler_types.h>. We
already have a mechanism to remove unused macros, so let's do that. We
don't currently have a way to remove unused #includes, so we still need
<linux/compiler.h> and <linux/compiler_types.h> files (but I've clarified
the comments in them).

I've kept the empty definitions of `__user` and `__force` for source
compatibility. (We had one security test at least that was assuming
a kernel struct definition will "just work".)

Bug: http://b/262917450
Test: treehugger
Change-Id: Iacbbbc1aeef9a4fac52dabd7811ab875cc267d4f
diff --git a/libc/kernel/uapi/linux/i2o-dev.h b/libc/kernel/uapi/linux/i2o-dev.h
index fc8b26d..afaae74 100644
--- a/libc/kernel/uapi/linux/i2o-dev.h
+++ b/libc/kernel/uapi/linux/i2o-dev.h
@@ -42,38 +42,38 @@
 };
 struct i2o_cmd_passthru {
   unsigned int iop;
-  void __user * msg;
+  void  * msg;
 };
 struct i2o_cmd_hrtlct {
   unsigned int iop;
-  void __user * resbuf;
-  unsigned int __user * reslen;
+  void  * resbuf;
+  unsigned int  * reslen;
 };
 struct i2o_cmd_psetget {
   unsigned int iop;
   unsigned int tid;
-  void __user * opbuf;
+  void  * opbuf;
   unsigned int oplen;
-  void __user * resbuf;
-  unsigned int __user * reslen;
+  void  * resbuf;
+  unsigned int  * reslen;
 };
 struct i2o_sw_xfer {
   unsigned int iop;
   unsigned char flags;
   unsigned char sw_type;
   unsigned int sw_id;
-  void __user * buf;
-  unsigned int __user * swlen;
-  unsigned int __user * maxfrag;
-  unsigned int __user * curfrag;
+  void  * buf;
+  unsigned int  * swlen;
+  unsigned int  * maxfrag;
+  unsigned int  * curfrag;
 };
 struct i2o_html {
   unsigned int iop;
   unsigned int tid;
   unsigned int page;
-  void __user * resbuf;
-  unsigned int __user * reslen;
-  void __user * qbuf;
+  void  * resbuf;
+  unsigned int  * reslen;
+  void  * qbuf;
   unsigned int qlen;
 };
 #define I2O_EVT_Q_LEN 32