clang-tidy: Remove old entries from blacklist

Now that clang-tidy-8 is used, we can remove the checks that have been
renamed.  Also enable a return-braced-init-list, because we don't have
any violations for that one.

.clang-tidy

@@ -7,9 +7,6 @@ bugprone-*,\
 -bugprone-too-small-loop-variable,\
 google-readability-casting,\
 misc-*,\
--misc-incorrect-roundings,\
--misc-macro-parentheses,\
--misc-misplaced-widening-cast,\
 -misc-non-private-member-variables-in-classes,\
 -misc-static-assert,\
 modernize-*,\
@@ -24,7 +21,6 @@ performance-*,\
 readability-*,\
 -readability-function-size,\
 -readability-identifier-naming,\
--readability-implicit-bool-cast,\
 -readability-implicit-bool-conversion,\
 -readability-inconsistent-declaration-parameter-name,\
 -readability-magic-numbers,\