Revert "prereq-build: check for "bc" (#13767)"

Makes all buildbot builds fail; until we get the right software
installed, revert this changeset.

Signed-off-by: Florian Fainelli <[email protected]>

SVN-Revision: 37122

include/prereq-build.mk

@@ -183,7 +183,3 @@ endef
 $(eval $(call Require,getopt-extended, \
 	Please install an extended getopt version that supports --long \
 ))
-
-$(eval $(call RequireCommand,bc, \
-	Please install bc. \
-))