PR 30569, delete _bfd_mips_elf_early_size_sections

PR30569 was triggered by a patch of mine 6540edd5 moving the call
to always_size_sections in bfd_elf_size_dynamic_sections earlier, made
to support the x86 DT_RELR implementation.  This broke mips16 code
handling stubs when --export-dynamic is passed to the linker, because
numerous symbols then became dynamic after always_size_sections.  The
mips backend fiddles with symbols in its always_size_sections.  Maciej
in 902e9fc7 had moved the call to always_size_sections to after
the export-dynamic code.  Prior to that, Nathan in 04c3a755 moved
it before the exec stack code, back to the start of
bfd_elf_size_dynamic_sections which was where Ian put it originally
in ff12f303.  So the call has moved around a little.  I'm leaving
it where it is, and instead calling mips_elf_check_symbols from
late_size_sections (the old size_dynamic_sections) which is now always
called.  In fact, the whole of _bfd_mips_elf_early_size_sections can
be merged into _bfd_mips_elf_late_size_sections.