[libcpu] remove libcpu/risc-v

bsp/hifive1/SConscript

@@ -1,18 +0,0 @@
-# for module compiling
-import os
-Import('RTT_ROOT')
-from building import *
-
-cwd = str(Dir('#'))
-src = Glob('*.c')
-objs = []
-list = os.listdir(cwd)
-
-for d in list:
-    path = os.path.join(cwd, d)
-    if os.path.isfile(os.path.join(path, 'SConscript')):
-        objs = objs + SConscript(os.path.join(d, 'SConscript'))
-
-group = DefineGroup('', src, depend = [''], CPPPATH = [])
-#objs += group
-Return('objs')