Remove some frame invalidation code

I stumbled across a few spots that mention that a function
"invalidates frame" and also assignments of NULL to a frame_info_ptr.
This code isn't harmful, but is also unnecessary since the
introduction of frame_info_ptr -- nowadays frame invalidations are
handled automatically.

Regression tested on x86-64 Fedora 38.

Approved-By: Simon Marchi <simon.marchi@efficios.com>