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>

tools/zstd/Makefile

@@ -12,7 +12,6 @@ PKG_LICENSE_FILES:=LICENSE
 PKG_CPE_ID:=cpe:/a:facebook:zstandard
 
 CMAKE_SOURCE_SUBDIR:=build/cmake
-HOST_BUILD_PARALLEL:=1
 
 include $(INCLUDE_DIR)/host-build.mk
 include $(INCLUDE_DIR)/cmake.mk