gdb/testsuite: remove unneeded calls to get_compiler_info

It is not necessary to call get_compiler_info before calling
test_compiler_info, and, after recent commits that removed setting up
the gcc_compiled, true, and false globals from get_compiler_info,
there is now no longer any need for any test script to call
get_compiler_info directly.

As a result every call to get_compiler_info outside of lib/gdb.exp is
redundant, and this commit removes them all.

There should be no change in what is tested after this commit.