build: Remove HAVE_PIPE_LOADER_SW.

It guarded the function prototype of pipe_loader_sw_probe, whose use (in
pipe_loader.c) and definition (in pipe_loader_sw.c) were not guarded.
Both are built into libpipe_loader.la if HAVE_LOADER_GALLIUM, which is
enable_gallium_loader in configure.ac.

Tested-by: Tom Stellard <thomas.stellard@amd.com>
Tested-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

configure.ac

@@ -1913,7 +1913,6 @@ AM_CONDITIONAL(NEED_GALLIUM_LLVMPIPE_DRIVER, test "x$HAVE_GALLIUM_I915" = xyes -
 
 if test "x$enable_gallium_loader" = xyes; then
     GALLIUM_WINSYS_DIRS="$GALLIUM_WINSYS_DIRS sw/null"
-    GALLIUM_PIPE_LOADER_DEFINES="-DHAVE_PIPE_LOADER_SW"
     GALLIUM_PIPE_LOADER_LIBS="\$(top_builddir)/src/gallium/auxiliary/pipe-loader/libpipe_loader.la"
 
     if test "x$NEED_WINSYS_XLIB" = xyes; then

src/gallium/auxiliary/pipe-loader/pipe_loader.h

@@ -99,8 +99,6 @@ pipe_loader_create_screen(struct pipe_loader_device *dev,
 void
 pipe_loader_release(struct pipe_loader_device **devs, int ndev);
 
-#ifdef HAVE_PIPE_LOADER_SW
-
 /**
  * Get a list of known software devices.
  *
@@ -111,8 +109,6 @@ pipe_loader_release(struct pipe_loader_device **devs, int ndev);
 int
 pipe_loader_sw_probe(struct pipe_loader_device **devs, int ndev);
 
-#endif
-
 #ifdef HAVE_PIPE_LOADER_DRM
 
 /**