gdb: Remove redundant frame switching

547ce8f0 fixed an issue where dynamic types were not being resolved
correctly prior to printing a value. The same issue was discovered when
printing the value using mi-mode, which was not covered by the fix.
Porting the fix to the mi-mode code path resolved the issue.

However, it was discovered that a later patch series, ending
2fc3b8a4, independently fixed the issue in both the cli- and mi-mode
code paths, making the original fix unneeded.

This commit removes this extra frame switch and adds test coverage for
the mi-mode scenario to protect against any future divergence in this
area.

GDB built with GCC 11.

No test suite regressions detected. Compilers: GCC 12.1.0, ACfL 22.1,
Intel 22.1; Platforms: x86_64, aarch64.

Approved-By: Tom Tromey <tom@tromey.com>