precompiled_header.h: remove chartTesting.h

[valgur]

The chartTesting.h header is no longer used anywhere in the codebase, but it causes a compilation error on MSVC when building with C++20 or newer:

C:\Users\martin\.conan2\p\b\gtsam83ef710337281\b\src\gtsam\base\chartTesting.h(42,3): error C3878: syntax error: unexpected token ')' following 'expression_statement' [C:\Users\martin\.conan2\p\b\gtsam83ef710337281\b\build\gtsam 
\gtsam.vcxproj]
  (compiling source file '../../src/gtsam/precompiled_header.cpp')

This PR removes it from the list of precompiled headers as a fix. Should the chartTesting.h header be removed altogether, perhaps?

Fixes #1788.

[ProfFan]

Thank you!