Remove Everest VS2010 compatibility headers

These headers were necessary for compatibility with Visual Studio 2010,
and interfere with the system headers on Visual Studio 2013+, eg. when
building Mbed TLS using the .sln file shipped with the project.

Move the still-required definition of "inline" to callconv.h, where the
definition for GCC also lives.

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>