posix: options: remove default setting of toolchain option

Do not set TC_PROVIDES_POSIX_C_LANG_SUPPORT_R as the default in
lib/posix/options/Kconfig.c_lang_r . TC_PROVIDES options are
only intended to be set by C libraries that implement parts of
the POSIX standard.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>