[analyzer][NFC] Fix some incorrect uses of -analyzer-config options

I'm in the process of refactoring AnalyzerOptions. The main motivation behind
here is to emit warnings if an invalid -analyzer-config option is given from
the command line, and be able to list them all.

In this patch, I found some flags that should've been used as checker options,
or have absolutely no mention of in AnalyzerOptions, or are nonexistent.

- NonLocalizedStringChecker now uses its "AggressiveReport" flag as a checker
    option
- lib/StaticAnalyzer/Frontend/ModelInjector.cpp now accesses the "model-path"
    option through a getter in AnalyzerOptions
- -analyzer-config path-diagnostics-alternate=false is not a thing, I removed it,
- lib/StaticAnalyzer/Checkers/AllocationDiagnostics.cpp and
    lib/StaticAnalyzer/Checkers/AllocationDiagnostics.h are weird, they actually
    only contain an option getter. I deleted them, and fixed RetainCountChecker
    to get it's "leak-diagnostics-reference-allocation" option as a checker option,
- "region-store-small-struct-limit" has a proper getter now.

Differential Revision: https://reviews.llvm.org/D53276

llvm-svn: 345985