gdal: don't link extra dylibs for vendored libkml

Since the extra libs `minizip` and `uriparser` are statically linked to vendored libkml, this keeps **configure** from testing for them (which fails unless they are installed otherwise).

I missed this on commit adding vendored libkml since I actually had `minizip` and `uriparser` packages installed, and that masked the issue.

The [issue is reported upstream](https://github.com/Homebrew/homebrew/blob/c90739084386b34beddc8215f43303a2dd52517f/Library/Formula/libkml.rb#L10-L20), i.e. allow linking to external libs, but no action on it.

I would also like to either add optional [vendored `openjpeg` 2 support](https://github.com/Homebrew/homebrew/pull/28526#issuecomment-42363336), or optionally `depends_on` a [new formula from homebrew-versions](https://github.com/Homebrew/homebrew-versions/pull/419). Should I wait on doing a _revision 1_ until that support is added as well?