treewide: remove BUILD_PARALLEL from CMake packages

It's already default. The only exception is mt76 which has Ninja
disabled.

Found with:

git grep BUILD_PARALLEL | cut -d ':' -f 1 | sort -u > par
git grep cmake.mk | cut -d ':' -f 1 > cmake
comm -1 -2 par cmake

Signed-off-by: Rosen Penev <rosenp@gmail.com>

package/system/opkg/Makefile

@@ -26,8 +26,6 @@ PKG_CONFIG_DEPENDS += \
 	CONFIG_SIGNATURE_CHECK \
 	CONFIG_TARGET_INIT_PATH
 
-PKG_BUILD_PARALLEL:=1
-HOST_BUILD_PARALLEL:=1
 PKG_INSTALL:=1
 
 HOST_BUILD_DEPENDS:=libubox/host

package/system/rpcd/Makefile

@@ -20,7 +20,6 @@ PKG_MIRROR_HASH:=69d9588a5a910676252eabcd2815af318806cae8316777e8b6eb00b26bdc42c
 PKG_LICENSE:=ISC
 PKG_LICENSE_FILES:=
 
-PKG_BUILD_PARALLEL:=1
 PKG_ASLR_PIE_REGULAR:=1
 
 include $(INCLUDE_DIR)/package.mk

package/system/uci/Makefile

@@ -22,7 +22,6 @@ PKG_LICENSE_FILES:=
 
 PKG_MAINTAINER:=Felix Fietkau <nbd@nbd.name>
 
-PKG_BUILD_PARALLEL:=0
 PKG_FLAGS := nonshared
 
 include $(INCLUDE_DIR)/package.mk

package/system/urngd/Makefile

@@ -12,8 +12,6 @@ PKG_MIRROR_HASH:=2d31025b79fe130c579d6c3f4bf4dc12abc43a7319b20a5cdca24ae363ec70f
 PKG_LICENSE:=GPL-2.0 BSD-3-Clause
 PKG_LICENSE_FILES:=
 
-PKG_BUILD_PARALLEL:=1
-
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk