bash re-enable parallel builds

They don't seem to be causing any issues after bumping to the 4.3.x
series and several tests.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/bash/bash.mk

@@ -22,10 +22,6 @@ BASH_CONF_ENV += \
 	bash_cv_func_sigsetjmp=present \
 	bash_cv_printf_a_format=yes
 
-# Parallel build sometimes fails because some of the generator tools
-# are built twice (i.e. while executing).
-BASH_MAKE = $(MAKE1)
-
 # The static build needs some trickery
 ifeq ($(BR2_STATIC_LIBS),y)
 BASH_CONF_OPTS += --enable-static-link --without-bash-malloc