[mips][test] Remove redundant and invalid `CHECK-NOT` directives. NFC

[mips][test] Remove redundant and invalid `CHECK-NOT` directives. NFC

1. It's redundant to explicitly check that string does not contain `PAUSE_MM`
   token if check that the `PAUSE` token is followed by an angle bracket.
2. The removed `CHECK-NOT` directives do not have trailing colons.