Remove pexpect and add a deprecation warning

[angelhof]

The pexpect import is no longer needed since it was only used to evaluate a slower configuration of PaSh. I removed pexpect from the installation and from everywhere in PaSh.

Signed-off-by: Konstantinos Kallas konstantinos.kallas@hotmail.com

[github-actions]

OS:ubuntu-20.04
Tue Sep 6 18:40:11 UTC 2022
intro: 2/2 tests passed.
interface: 39/39 tests passed.
compiler: 54/54 tests passed.
agg: 109/109 tests passed.

[github-actions]

OS = Debian 10
CPU = Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
Ram = 15752
Hash = 6f95b2d
Kernel= Linux 4.15.0-167-generic x86_64

benchmark	tests	passed	failed	untested	unresolved	unsupported	not_in_use	other_status
posix	494	375	41	31	6	40	1	0
intro	2	2	0	0	0	0	0	0
interface	39	39	0	0	0	0	0	0
compiler	54	54	0	0	0	0	0	0
aggregator	109	108	1	0	0	0	0	0