treewide: remove PKG_INSTALL from CMake packages

It's already default with cmake.mk

Found with:

git grep PKG_INSTALL\: | cut -d ':' -f 1 | sort -u > ins
git grep cmake.mk | cut -d ':' -f 1 > cmake
comm -1 -2 ins cmake

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

package/libs/mbedtls/Makefile

@@ -87,8 +87,6 @@ This package contains mbedtls helper programs for private key and
 CSR generation (gen_key, cert_req)
 endef
 
-PKG_INSTALL:=1
-
 TARGET_CFLAGS += -ffunction-sections -fdata-sections
 TARGET_CFLAGS := $(filter-out -O%,$(TARGET_CFLAGS))