tests/feature_check/tstring.py: Remove check for string.templatelib.

If a port enables t-strings then it is required to have the
`string.templatelib` package (at least to run the tests).  That's
automatically the case if `MICROPY_PY_TSTRINGS` is enabled.

If a port freezes in the micropython-lib `string` extension package then
the latest version of this package will include the built-in
`string.templatelib` classes.  So the feature check for t-strings no longer
needs to check if they are available.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

tests/feature_check/tstring.py

@@ -1,8 +1,5 @@
 # check whether t-strings (PEP-750) are supported
 
-# TODO remove this check when micropython-lib's string extends ustring
-from string.templatelib import Template, Interpolation
-
 a = 1
 t = t"a={a}"
 print("tstring")