tcg: Remove TODO file

The last update to this file was 9 years ago.  In the meantime,
4 of the 6 ideas have actually been completed.  The lat two do
not actually make sense anymore.
Suggested-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>

tcg/TODO

-- Add new instructions such as: clz, ctz, popcnt.
-
-- See if it is worth exporting mul2, mulu2, div2, divu2. 
-
-- Support of globals saved in fixed registers between TBs.
-
-Ideas:
-
-- Move the slow part of the qemu_ld/st ops after the end of the TB.
-
-- Change exception syntax to get closer to QOP system (exception
-  parameters given with a specific instruction).
-
-- Add float and vector support.