libgeotiff: relocatable shared lib on macOS

[SpaceIm]

see conan-io/hooks#376

Since I had to patch upstream CMakeLists to allow relocatable libs, I've taken advantage if this PR to modernize (and simplify) a little bit the patches in order to rely on cmake_find_package* generators instead of CONAN_LIBS.

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• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[conan-center-bot]

All green in build 3 (29f9be45f3f8496e39b1180d07fb25038ea4cffd):

• libgeotiff/1.6.0@:
  All packages built successfully! (All logs)

• libgeotiff/1.7.0@:
  All packages built successfully! (All logs)

• libgeotiff/1.5.1@:
  All packages built successfully! (All logs)