build: Don't build pipebuffer

It's already built by src/gallium/auxiliary.

src/gallium/auxiliary/Makefile.am

@@ -3,7 +3,6 @@ AUTOMAKE_OPTIONS = subdir-objects
 include Makefile.sources
 include $(top_srcdir)/src/gallium/Automake.inc
 
-SUBDIRS += pipebuffer
 noinst_LTLIBRARIES = libgallium.la
 
 AM_CFLAGS = \

src/gallium/auxiliary/pipebuffer/Makefile

@@ -1,18 +0,0 @@
-TOP = ../../../..
-include $(TOP)/configs/current
-
-LIBNAME = pipebuffer
-
-C_SOURCES = \
-	pb_buffer_fenced.c \
-	pb_buffer_malloc.c \
-	pb_bufmgr_alt.c \
-	pb_bufmgr_cache.c \
-	pb_bufmgr_debug.c \
-	pb_bufmgr_mm.c \
-	pb_bufmgr_ondemand.c \
-	pb_bufmgr_pool.c \
-	pb_bufmgr_slab.c \
-	pb_validate.c
-
-include ../../Makefile.template