cmake: don't set CL_INCLUDE_DIR in CMakeVendor.txt

This will always override anything the user provides. We could
turn it into a cache variable to avoid this but the default
value assumes the location of headers in a hypothetical driver
tree which probably doesn't work for anybody so just get rid of
it instead.

Also remove all references to OPENCL_DRIVER in the build system.
Any such integration doesn't really belong in the CTS's build
system and can trivially be done with a wrapper project.

Signed-off-by: Kevin Petit <kevin.petit@arm.com>

CMakeVendor.txt

@@ -1,8 +1,3 @@
-# Include cmake files to build driver
-# to build driver as a dependency of tests
-# in this example environment variable $OPENCL_DRIVER points to driver base
-# Ex  include($ENV{OPENCL_DRIVER}/driver.cmake)
-
 # We intentionally hardcode "_win32" to ensure backwards compatibility (to avoid breaking HAAVE)
 if(ANDROID)
    if(ARM64_V8A)
@@ -11,5 +6,3 @@ if(ANDROID)
        set(ARCH "32")
    endif(ARM64_V8A)
 endif (ANDROID)
-
-set (CL_INCLUDE_DIR "$ENV{OPENCL_DRIVER}/include/public/")