Remove "static inline" from qtro_ functions

Functions in headers shouldn't be marked as static, because that
prevents deduplication at link-time. As function templates, they also
don't need to be marked as inline, as that's the default linkage for
function templates, anyway.

Amends 7cc03eac6fb5aa7bcb91201f5ce3251049ad0bbb (5.9.8) and
c96a4193e5d4d46804e8a11fad3b0e95d02b037b (5.12.4).

Pick-to: 6.12 6.11 6.8
Change-Id: I42c7d5fe8e0de928a03c611eb441b30347351d35
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>