[clang-tidy][NFCI] DanglingHandleCheck: Remove a superflous IgnoreParenImpCasts

ExprWithCleanups is currently not skipped by IgnoreParenImpCasts, but is skipped
by IgnoreImpCasts. In view of fixing this inconsistency in D57267, remove the
IgnoreParenImpCasts between the ReturnStmt and the ExprWithCleanups which
is not needed since ExprWithCleanups is always created as a direct child of
ReturnStmt (by inspection of each ReturnStmt::Create in Sema/SemaStmt.cpp).

NFC intended.

llvm-svn: 354228