[TLI] Remove leftover assert in TargetLibraryInfoImpl initialize (#79056)

Remove unnecessary assert for a sorted StandardNames after
implementation of getLibFunc is changed from binary search to a DenseMap
Lookup in commit 7d950f04.

The original getLibFunc binary search implementation is in commit
c740e3f0.

Co-authored-by: Tony Tao <tonytao@ca.ibm.com>