Remove pre-Python-3.4 compatibility from build-many-glibcs.py.

Remove pre-Python-3.4 compatibility from build-many-glibcs.py.

Since we have consensus on requiring Python 3.4 or later to build
glibc, it follows that compatibility with older Python versions is
also no longer relevant to auxiliary Python scripts for use in glibc
development.  This patch removes such compatibility code from
build-many-glibcs.py (compatibility code needed for 3.4, which lacks
the newer subprocess interface, is kept).  Because
build-many-glibcs.py is not itself called from the glibc build system,
this patch is independent of the configure checks for having a
new-enough Python version, which are only relevant to uses of Python
from the main build and test process.

Tested with build-many-glibcs.py building glibc for aarch64-linux-gnu
(with Python 3.4 to make sure that still works).

	* scripts/build-many-glibcs.py: Remove compatibility for missing
	os.cpu_count and re.fullmatch.