C++: Remove @precision from AV Rule 78
C++: Remove @precision from AV Rule 78

This rule, named "No virtual destructor", was supposed to be superseded
by `cpp/virtual-destructor` in 0c796de83, but that commit didn't
actually disable this rule, so both rules are now active in the LGTM
suite.

This commit disables the rule by removing `@precision`. We're still
discussing the best way to disable rules that are precise and valid but
not universally applicable. For now, removing `@precision` is consistent
with how we're keeping most other JSF queries from appearing on LGTM.

github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql