[clangd] Simplify code using findName. NFC

`findName` was always used in conjuction with `spellingLocIfSpelled`.
This patch replaces patterns of the form:
  spellingLocIfSpelled(findName(&ND), SM)

With a new helper function:
  nameLocation(ND, SM)

And removes `spellingLocIfSpelled` and `findName`. Both are never used
anywhere else and the latter is an equivalent of `Decl::getLocation` if
we ever need it again.