Kill environment.is_*

[bonzini]

    def is_header(self, fname: 'mesonlib.FileOrString') -> bool:
        return is_header(fname)

    def is_source(self, fname: 'mesonlib.FileOrString') -> bool:
        return is_source(fname)

    def is_assembly(self, fname: 'mesonlib.FileOrString') -> bool:
        return is_assembly(fname)

    def is_separate_compile(self, fname: 'mesonlib.FileOrString') -> bool:
        return is_separate_compile(fname)

    def is_llvm_ir(self, fname: 'mesonlib.FileOrString') -> bool:
        return is_llvm_ir(fname)

    def is_object(self, fname: 'mesonlib.FileOrString') -> bool:
        return is_object(fname)

    @lru_cache(maxsize=None)
    def is_library(self, fname: mesonlib.FileOrString) -> bool:
        return is_library(fname)

These have no state, so just use the version in compilers?