meson: Drop tcg as a module

meson: Drop tcg as a module

This reverts commit dae0ec159f9 ("accel: build tcg modular").
The attempt was only enabled for x86, only modularized a small
portion of tcg, and in more than 3 years there have been no
follow-ups to improve the situation.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>