Mostly old build scripts and helper files that are now covered by the
Makefile.
A notable deletion is the glew dll and lib files. These are unnecessary
because we compile `glew.c` directly rather than link against the dll or
lib copies we have.
If a user has Homebrew installed, calling g++ won't use Apple's Xcode version of the tool, which is required by QB64. This fix continues on with the patch introduced in 4dbdddc89e.
Extra "osx" references replaced with "macOS", but nothing substantial (almost aesthetic).
