[lldb] Remove some trivial scoped timers

While profiling lldb (from swift/llvm-project), these timers were noticed to be short lived and high firing, and so they add noise more than value.

The data points I recorded are:

`FindTypes_Impl`: 49,646 calls, 812ns avg, 40.33ms total
`AppendSymbolIndexesWithName`: 36,229 calls, 913ns avg, 33.09ms total
`FindAllSymbolsWithNameAndType`: 36,229 calls, 1.93µs avg, 70.05ms total
`FindSymbolsWithNameAndType`: 23,263 calls, 3.09µs avg, 71.88ms total

Differential Revision: https://reviews.llvm.org/D115182