ui/cocoa: Drop tests for CGImageCreateWithImageInRect support

ui/cocoa: Drop tests for CGImageCreateWithImageInRect support

The code that tries to test at both compiletime and runtime
for whether CGImageCreateWithImageInRect is supported provokes
a compile warning on OSX 10.3:

ui/cocoa.m:378:13: warning: comparison of function 'CGImageCreateWithImageInRect'
      equal to a null pointer is always false[-Wtautological-pointer-compare]
        if (CGImageCreateWithImageInRect == NULL) { // test if "CGImageCreateWithImageInRect" is
supported on host at runtime
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~    ~~~~

The simplest way to deal with this is just to drop this code,
since we don't in practice support OSX 10.4 anyway. (10.5 was
released in 2007 and is the last PPC version, so is the earliest
we really need to continue to support at all.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1431296361-16981-2-git-send-email-peter.maydell@linaro.org